fix: drop reflective access warnings to java.time.* classes (#596)

Java module system gives warnings on reflective access to java.time.*
private fields, which are performed by Jackson when using
TwilioRestClient.

Jackson provides a `JavaTimeModule` which configures an ObjectMapper to
use public methods instead of reflective access to private fields in
classes in java.time.

This PR adds the dependency for `JavaTimeModule` and adds it to the
ObjectMapper created by `TwilioRestClient`, which removes all the
warnings that I have seen.

pom.xml

@@ -204,6 +204,11 @@
       <artifactId>jackson-databind</artifactId>
       <version>${jackson.version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.datatype</groupId>
+      <artifactId>jackson-datatype-jsr310</artifactId>
+      <version>${jackson.version}</version>
+    </dependency>
     <dependency>
       <groupId>javax.xml.bind</groupId>
       <artifactId>jaxb-api</artifactId>

src/main/java/com/twilio/http/TwilioRestClient.java

@@ -1,6 +1,7 @@
 package com.twilio.http;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 
 import java.util.function.Predicate;
 
@@ -27,6 +28,12 @@ private TwilioRestClient(Builder b) {
         this.edge = b.edge;
         this.httpClient = b.httpClient;
         this.objectMapper = new ObjectMapper();
+
+        // This module configures the ObjectMapper to use
+        // public API methods for manipulating java.time.*
+        // classes. The alternative is to use reflection which
+        // generates warnings from the module system on Java 9+
+        objectMapper.registerModule(new JavaTimeModule());
     }
 
     /**