Change olm dependency to normal dep

It would be nice if it were actually an optional dependency and you
could just not install olm and get a Riot without olm, but you can't:
what you get is a broken Riot, so having it as an optional dep isn't
helping anyone.

Also whatever other package-lock changes npm has decided are
necessary today.

package.json

@@ -73,6 +73,7 @@
     "matrix-js-sdk": "1.0.1",
     "matrix-react-sdk": "1.0.3",
     "modernizr": "^3.6.0",
+    "olm": "https://matrix.org/packages/npm/olm/olm-3.1.0-pre1.tgz",
     "prop-types": "^15.6.2",
     "react": "^15.6.0",
     "react-dom": "^15.6.0",
@@ -147,9 +148,7 @@
     "webpack-cli": "^3.1.2",
     "webpack-dev-server": "^3.1.10"
   },
-  "optionalDependencies": {
-    "olm": "https://matrix.org/packages/npm/olm/olm-3.1.0-pre1.tgz"
-  },
+  "optionalDependencies": {},
   "build": {
     "appId": "im.riot.app",
     "electronVersion": "4.0.6",