Update ruby-mocha to 1.9.0.
## 1.9.0
* Add TruffleRuby to Travis CI build matrix - thanks to @deepj (#354)
* Explicitly set Travis CI OS to Ubuntu Trusty 14.04 (ded1fa45)
* Expand explanation of thread-safety concerns - thanks to @techbelly (#357)
* Refactor class method and any instance method - thanks to @chrisroos (#358)
* Rely on default bundler version in Travis CI builds (3352e9c5)
* Fix local build-matrix script (11abe231)
* No need to install latest bundler in build-matrix script (8247a894)
498aa91c0a