Update .travis.yml

- openjdk6
Fixes #65. NoMainMethodInAbstractClassCheck was introduced.
Merge pull request #119 from baratali/master

NoMainMethodInAbstractClassCheck
fix for #122
Merge pull request #123 from isopov/ISSUE-122

fix for #122
Alexander Berezovsky was added
Avoid Constant As First Operand In Condition Check
Merge pull request #120 from burtsevsergey/null-condition

"Avoid Constant As First Operand In Condition Check" was merged
SergeyBurtsev was added
SimpleAccessorNameNotationCheck fixed
Merge pull request #124 from sabaka/iss74

SimpleAccessorNameNotationCheck fixed
Update README.textile
NoNullForCollectionReturnCheck created
Merge pull request #126 from sabaka/iss63

NoNullForCollectionReturnCheck created
Fixes #75. ForbidWildcardAsReturnTypeCheck was introduced.
Merge pull request #127 from baratali/iss75

Fixes #75. ForbidWildcardAsReturnTypeCheck was introduced.
lib/tools.jar has been deleted.
Issue #90: Confusing Termary. fixed
Merge pull request #129 from baratali/iss118

Fixes #118. lib/tools.jar has been deleted from pom.xml.
Issue #90: Confusing Termary. fixed2