Add Travis CI build status image.
Add Travis CI build status image.

Added the Travis CI build status image to show the current build status.

flaxandteal/stapler,oschettler/stapler,neerajgoyal12/stapler,InMoji/stapler,aozisik/stapler,sonuku/stapler,riyan8250/stapler,simudream/stapler,CodeSleeve/stapler,AndreasHeiberg/stapler