Bump Checker Framework annotations version to 2.5.2.

Fixes #467 for Truth and perhaps similar problems for other projects that use Guava.

RELNOTES: Updated to versions of the Checker Framework annotations packages that don't contain conflicting classes.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=201097814

core/pom.xml

@@ -15,7 +15,7 @@
     <gwt.version>2.8.2</gwt.version>
     <junit.version>4.12</junit.version>
     <diffutils.version>1.3.0</diffutils.version>
-    <checker-framework.version>2.0.0</checker-framework.version>
+    <checker-framework.version>2.5.2</checker-framework.version>
     <auto-value.version>1.5.3</auto-value.version>
     <compile-testing.version>0.15</compile-testing.version>
     <error-prone.annotations.version>2.2.0</error-prone.annotations.version>