[lab] Depend on @babel/runtime. (#12470)

@babel/runtime will also be installed by the peerDependency on @material-ui/core, but it might also
be installed by some other module or by the consuming app. That means the @babel/runtime that will
actually be resolved by @material-ui/lab is not guaranteed to be the same as the one resolved by
core, without an explicit dependency.

In particular, I was installing @babel/runtime@7.0.0-rc.1 in my app, which has different file paths
from beta.42, causing imports of @babel/runtime from @material-ui/lab to fail.

This patch ensures a compatible version of the runtime is always used.

packages/material-ui-lab/package.json

@@ -38,7 +38,9 @@
     "react": "^16.3.0",
     "react-dom": "^16.3.0"
   },
-  "dependencies": {},
+  "dependencies": {
+    "@babel/runtime": "7.0.0-beta.42"
+  },
   "devDependencies": {},
   "sideEffects": false,
   "publishConfig": {