gradle changes: version upgrades (gradle and gradle plugins); URL's are changed (http -->> to https) for artifact repositories and also for some javadoc links

details:

gradle: 4.6 -->> 5.6.2; also, gradle wrapper is now using gradle distribution with sources (that provides IDE with gradle API/DSL documentation)
build script dependencies version upgrades:
- 'io.spring.gradle:propdeps-plugin' 0.0.9 -->> 0.0.10
- 'org.jfrog.buildinfo:build-info-extractor-gradle' 3.0.1 -->> 4.9.9
- 'com.typesafe:config' 1.2.1 -->> 1.3.4
plugin dependencies version upgrades:
- 'com.github.kt3k.coveralls' 2.6.3 -->> 2.8.4
- 'com.jfrog.bintray' 1.0 -->> 1.8.4
- 'org.ajoberstar.grgit' 2.2.0 -->> 3.1.1
github-test.prop: 'GitHubTests.commit' values is changed (to a more recent value)

note: Gradle 5.x introduces default values for Xmx anx Xms (see DEFAULT_JVM_OPTS in gradlew and gradlew.bat files):
- https://docs.gradle.org/5.6.2/userguide/upgrading_version_4.html#rel5.0:default_memory_settings
- keep in mind these values can be controlled via gradle.properties; example: org.gradle.jvmargs=-Xms1024m -Xmx1024m https://docs.gradle.org/5.6.2/userguide/build_environment.html https://docs.gradle.org/5.6.2/dsl/org.gradle.api.tasks.JavaExec.html#org.gradle.api.tasks.JavaExec:jvmArgs

ethereum / ethereumj