Restrict the versions and add 3.1

'~> 2.6' will match 2.7.x.
Merge pull request #155 from richardc/patch-1

Restrict the versions and add 3.1
fix mocha deprecation warnings
Merge pull request #156 from mattr-/fix-mocha-warnings

fix mocha deprecation warnings
Adding php bindings to readme
Merge pull request #158 from ke4qqq/patch-1

Adding php bindings to readme