upgrade gradle wrapper to 4.4 (#158)

Author: wangjoshuah

gradle/wrapper/gradle-wrapper.jar

@@ -1,6 +1,5 @@
-#Tue Feb 23 16:11:46 PST 2016
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-2.10-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-bin.zip