Fix java.lang.NoClassDefFoundError on gradlew :imgui-lwjgl3:startExample

See https://stackoverflow.com/questions/61289461/java-lang-noclassdeffounderror-could-not-initialize-class-org-codehaus-groovy-v
and https://github.com/gradle/gradle/issues/10248

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 #Sat Dec 14 22:33:02 MSK 2019
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.3-bin.zip
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStorePath=wrapper/dists