Fix variable escaping

Author: TheAssassin

travis/build-appimage.sh

@@ -21,7 +21,7 @@ cleanup () {
 trap cleanup EXIT
 
 # store repo root as variable
-REPO_ROOT=$(readlink -f $(dirname $(dirname $0)))
+REPO_ROOT=$(readlink -f $(dirname $(dirname "$0")))
 OLD_CWD=$(readlink -f .)
 
 pushd "$BUILD_DIR"