Update to Gradle 3.2.

- Update gradle-wrapper.properties.

Test: cd tools && ./gradlew test
Change-Id: I820b5a7cf1b95332938ead02faf300f11f571815
diff --git a/wrapper/gradle-wrapper.properties b/wrapper/gradle-wrapper.properties
index 0039d62..895c3c6 100644
--- a/wrapper/gradle-wrapper.properties
+++ b/wrapper/gradle-wrapper.properties
@@ -3,4 +3,4 @@
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=../../external/gradle/gradle-3.1-bin.zip
+distributionUrl=../../external/gradle/gradle-3.2-bin.zip