[Java] Upgrade to Checkstyle 7.6.

Author: mjpt777

build.gradle

@@ -116,7 +116,7 @@ subprojects {
     [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
 
     dependencies {
-        checkstyle 'com.puppycrawl.tools:checkstyle:7.5.1'
+        checkstyle 'com.puppycrawl.tools:checkstyle:7.6'
         checkstyle 'com.github.sevntu.checkstyle:sevntu-checks:1.23.0'
 
         testCompile 'org.hamcrest:hamcrest-all:1.3'
@@ -127,7 +127,7 @@ subprojects {
 
     checkstyle {
         configFile = new File(rootDir, 'config/checkstyle/checkstyle.xml')
-        toolVersion = '7.5.1'
+        toolVersion = '7.6'
     }
 
     compileJava {