Use latest 3.4 sass specs for travis CI build

Author: mgreter

script/bootstrap

@@ -6,7 +6,7 @@ script/branding
 : ${SASS_SASSC_PATH:="sassc" }
 
 if [ ! -d $SASS_SPEC_PATH ]; then
-  git clone https://github.com/sass/sass-spec.git $SASS_SPEC_PATH
+  git clone https://github.com/sass/sass-spec.git $SASS_SPEC_PATH --branch 3.4
 fi
 if [ ! -d $SASS_SASSC_PATH ]; then
   git clone https://github.com/sass/sassc.git $SASS_SASSC_PATH