Upgrade to Checkstyle 7.1.2

Bug fixes:

    Wrong order of "default" method modifier. Author: alberto.cuda #3471
    EqualsHashCode: hashCode without equals is not a violation. Author: rnveach #3308

Notes:

    Revert "Pull #3162: Update version of commons-collections to 3.2.2 to fix security vulnerability CVE-2015-6420". Author: Roman Ivanov
    Cut down on Checkstyle's dependencies on Guava. Author: Andrei Selkin #3433
    doc: fixed the wording in javadoc for TrailingCommentCheck. Author: José Castro
    doc: added missing slash to backport documentation url (#3457). Author: rnveach
    doc: added links to cs backport jre6 (#3447). Author: rnveach
    Replace line-based suppressions with inline ones for Checkstyle's suppressions.xml. Author: Andrei Selkin #2226
    Update Checkstyle GUI in order to display Javadoc tokens. Author: Baratali Izmailov #408
    Fix ForbidCertainImports config. Author: Andrei Selkin #3412
    use CyclomaticComplexity.switchBlockAsSingleDecisionPoint in checkstyle_checks.xml. Author: Andrei Selkin #2874
    SuppressCommentFilter not working with ClassDataAbstractionCoupling when specified on class. Author: Andrei Selkin #977
    Resolve IntelijIdea inspection violations for java8. Author: Mariia Mykhailova #3233
    Replace Guava's Joiner with Java 8 native approach. Author: Andrei Selkin #3406
    Fix grammar in issue templates. Author: Roman Ivanov #3428
    spelling: PR instructions, YOU --> YOUR. Author: Elliotte Rusty Harold