Update to Gradle 4.1 and shadowJar 4.0.4

Gradle 5.x requires a newer version of the shadow jar plugin.

Test: ./gradlew shadowJar
Bug: N/A
Change-Id: I1b2603be123a4c1b36fbcb08fefbdcc0cdfc7650
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 7e98c33..eb78b8e 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -4,4 +4,4 @@
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.0-milestone-1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.1-all.zip