Fixed travis build

Author: kevzlou7979

.travis.yml

@@ -12,7 +12,7 @@ before_install:
 - mvn install -DskipTests=true -DdryRun=true
 - cd ..
 # install the gwt-material library before we build the demo
-- git clone -b release_2.1 https://github.com/GwtMaterialDesign/gwt-material.git
+- git clone -b master https://github.com/GwtMaterialDesign/gwt-material.git
 - cd master
 - mvn install -DskipTests=true -DdryRun=true
 - cd ..