install davclient via https because travis fails to install via ssh

bower.json

@@ -26,7 +26,7 @@
     "requirejs": "2.2.0",
     "text": "^2.0.14",
     "underscore": "~1.8.3",
-    "davclient.js": "git@github.com:evert/davclient.js.git",
+    "davclient.js": "https://github.com/evert/davclient.js.git",
     "es6-promise": "^3.2.1",
     "ical.js": "^1.2.1"
   }