Add Travis to README.
Add Travis to README.

Resolves #21

kristianmandrup/babel-library-boilerplate,thejameskyle/generator-es6-library-boilerplate,pdougall1/arduino-javascript,kristianmandrup/babel-library-boilerplate,lanetix/generator-lanetix-script,michaelBenin/babel-library-boilerplate,joshbedo/babel-library-boilerplate,alex-wilmer/generator-babel-boilerplate,pdougall1/arduino-javascript,babel/babel-library-boilerplate,jasonblanchard/babel-library-boilerplate,paulfalgout/babel-library-boilerplate,justengland/babel-library-boilerplate,jasonblanchard/babel-library-boilerplate,justengland/babel-library-boilerplate,alex-wilmer/generator-babel-boilerplate,michaelBenin/babel-library-boilerplate,babel/generator-babel-boilerplate,babel/babel-library-boilerplate,megawac/generator-es6-library-boilerplate,nicksrandall/koto-starter,megawac/generator-es6-library-boilerplate,paulfalgout/babel-library-boilerplate,nicksrandall/koto-starter,joshbedo/babel-library-boilerplate,thejameskyle/generator-es6-library-boilerplate,babel/generator-babel-boilerplate