[Java] Upgrade to Checkstyle 7.0.

Author: mjpt777

build.gradle

@@ -115,7 +115,8 @@ subprojects {
     [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
 
     dependencies {
-        checkstyle "com.github.sevntu.checkstyle:sevntu-checks:1.21.0"
+        checkstyle 'com.puppycrawl.tools:checkstyle:7.0'
+        checkstyle 'com.github.sevntu.checkstyle:sevntu-checks:1.21.0'
 
         testCompile 'org.hamcrest:hamcrest-all:1.3'
         testCompile 'junit:junit:4.12'
@@ -125,7 +126,7 @@ subprojects {
 
     checkstyle {
         configFile = new File(rootDir, 'config/checkstyle.xml')
-        toolVersion = "6.19"
+        toolVersion = '7.0'
     }
 
     compileJava {