Update docs to use Kubernetes 1.17 as the minimum version

As of v0.20, Tekton Pipelines requires Kubernetes 1.17
(https://github.com/tektoncd/pipeline/releases/tag/v0.20.0), but the
docs were not updated. This updates all references of Kubernetes 1.16 to
1.17 as necessary.

DEVELOPMENT.md

@@ -153,7 +153,7 @@ _Adding the `upstream` remote sets you up nicely for regularly
 
 The recommended configuration is:
 
--   Kubernetes version 1.16 or later
+-   Kubernetes version 1.17 or later
 -   4 vCPU nodes (`n1-standard-4`)
 -   Node autoscaling, up to 3 nodes
 -   API scopes for cloud-platform
@@ -174,7 +174,7 @@ The recommended configuration is:
     variable (e.g. `PROJECT_ID`).
 
 1.  Create a GKE cluster (with `--cluster-version=latest` but you can use any
-    version 1.16 or later):
+    version 1.17 or later):
 
     ```bash
     export PROJECT_ID=my-gcp-project
@@ -192,7 +192,7 @@ The recommended configuration is:
      --machine-type=n1-standard-4 \
      --image-type=cos \
      --num-nodes=1 \
-     --cluster-version=1.16
+     --cluster-version=1.17
     ```
 
     Note that

README.md

@@ -30,8 +30,8 @@ Tekton Pipelines are **Typed**:
 - Jump in with [the tutorial!](docs/tutorial.md)
 - Take a look at our [roadmap](roadmap.md)
 
-*Note that starting from the 0.11 release of Tekton, you need to have
-a cluster with **Kubernetes version 1.16 or later***.
+*Note that starting from the 0.20 release of Tekton, you need to have
+a cluster with **Kubernetes version 1.17 or later***.
 
 ### Read the docs
 

docs/api-spec.md

@@ -42,7 +42,7 @@ This document makes reference in a few places to different profiles for Tekton i
 
 The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119).
 
-There is no formal specification of the Kubernetes API and Resource Model. This document assumes Kubernetes 1.16 behavior; this behavior will typically be supported by many future Kubernetes versions. Additionally, this document may reference specific core Kubernetes resources; these references may be illustrative (i.e. an implementation on Kubernetes) or descriptive (i.e. this Kubernetes resource MUST be exposed). References to these core Kubernetes resources will be annotated as either illustrative or descriptive.
+There is no formal specification of the Kubernetes API and Resource Model. This document assumes Kubernetes 1.17 behavior; this behavior will typically be supported by many future Kubernetes versions. Additionally, this document may reference specific core Kubernetes resources; these references may be illustrative (i.e. an implementation on Kubernetes) or descriptive (i.e. this Kubernetes resource MUST be exposed). References to these core Kubernetes resources will be annotated as either illustrative or descriptive.
 
 ## Modifying This Specification
 

docs/install.md

@@ -14,7 +14,7 @@ This guide explains how to install Tekton Pipelines. It covers the following top
 
 ## Before you begin
 
-1. You must have a Kubernetes cluster running version 1.16 or later.
+1. You must have a Kubernetes cluster running version 1.17 or later.
 
    If you don't already have a cluster, you can create one for testing with `kind`.
    [Install `kind`](https://kind.sigs.k8s.io/docs/user/quick-start/#installation) and create a cluster by running [`kind create cluster`](https://kind.sigs.k8s.io/docs/user/quick-start/#creating-a-cluster). This

docs/podtemplates.md

@@ -6,7 +6,7 @@ weight: 12
 -->
 # Pod templates
 
-A Pod template defines a portion of a [`PodSpec`](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.16/#pod-v1-core)
+A Pod template defines a portion of a [`PodSpec`](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.17/#pod-v1-core)
 configuration that Tekton can use as "boilerplate" for a Pod that runs your `Tasks` and `Pipelines`.
 
 You can specify a Pod template for `TaskRuns` and `PipelineRuns`. In the template, you can specify custom values for fields governing