Add a space to the Flutter SDK path on Travis (#14613)

Ensures we don't regress https://github.com/flutter/flutter/issues/6577.

dev/bots/travis_setup.sh

@@ -49,6 +49,13 @@ if [ -n "$TRAVIS" ]; then
   fi
 fi
 
+# rename the SDK directory to include a space
+echo "Renaming Flutter checkout directory to 'flutter sdk'"
+cd ..
+mv flutter flutter\ sdk
+cd flutter\ sdk
+echo "SDK directory is: $PWD"
+
 # disable analytics on the bots and download Flutter dependencies
 ./bin/flutter config --no-analytics