add dependency for travis

Author: facchinm

.travis.yml

@@ -11,6 +11,7 @@ install:
   - go get golang.org/x/tools/cmd/cover
   - go get github.com/mattn/goveralls
   - go get github.com/wadey/gocovmerge
+  - go get github.com/blang/semver
 
 script:
   - go build -v arduino.cc/arduino-builder