Merge pull request #952 from square/renovate/compile-testing.version

Update dependency com.google.testing.compile:compile-testing to v0.21.0

Author: JakeWharton

pom.xml

@@ -23,7 +23,7 @@
     <java.version>1.8</java.version>
     <junit.version>4.13.2</junit.version>
     <truth.version>1.1.3</truth.version>
-    <compile-testing.version>0.19</compile-testing.version>
+    <compile-testing.version>0.21.0</compile-testing.version>
   </properties>
 
   <scm>