Work around plugin-publish bug

The plugin-publish plugin is incompatible with Gradle 4.3. The earliest version
it works with is Gradle 4.10.3, so upgrade our build to that version. The integ
tests still run against 4.3, ensuring we don't regress in our compatibility.

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.3-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.3-bin.zip