chore: migrate builds to github actions

Setup GitHub action to compile assets on push.

Note that builds now append GitHub SHA as version meta instead of build number

.github/workflows/gradle.yml

@@ -0,0 +1,23 @@
+name: Java CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up JDK 1.8
+      uses: actions/setup-java@v1
+      with:
+        java-version: 1.8
+    - name: Build with Gradle
+      run: ./gradlew build
+    - name: Publish Artifacts
+      uses: actions/upload-artifact@master
+      with:
+        name: libs
+        path: build/libs
+

build.gradle

@@ -39,13 +39,13 @@ minecraft {
     mappings = config.mappings
     runDir = "run"
 
-    // Try appending the build number first
-    if (System.getenv("BUILD_NUMBER") != null) {
-        project.version += ".${System.getenv("BUILD_NUMBER")}"
+    // Try appending the github sha first
+    if (System.getenv("GITHUB_SHA") != null) {
+        project.version += "+${System.getenv("GITHUB_SHA").substring(0,7)}"
 
     // If that doesn't work, just append "SNAPSHOT"
     } else {
-        project.version += "-SNAPSHOT"
+        project.version += "+SNAPSHOT"
     }
 
     // replacing stuff in the source