android build: Use our patched react-native-webview to cut noise in log.

I've just made this "fork" repo, and a `zulip` branch in it, in order
to make a fix for a noisy bit of logging that was showing up even in
`tools/test android`, where we suppress non-error logs.

This commit zulip/react-native-webview#49aca8206 consists of a single
small patch atop v5.12.1, which we had been using.

I sent the fix as a PR upstream:
  react-native-webview/react-native-webview#844
which was promptly merged (thanks, upstream maintainers!), and
even promptly released, as 7.0.3.  We're still on 5.x until we
deal with the RN upgrade to v0.60 (#3548), so for now we stick
the patch in this small fork-branch of our own.

(This is one of those times I really wish we had comments in
package.json. :-/  The key information in this commit message
really ought to be in a 1- or 2-line comment in the file.)

package.json

@@ -62,7 +62,7 @@
     "react-native-sound": "^0.10.9",
     "react-native-text-input-reset": "^1.0.2",
     "react-native-vector-icons": "^4.6.0",
-    "react-native-webview": "^5.0.0",
+    "react-native-webview": "git://github.com/zulip/react-native-webview#49aca8206",
     "react-navigation": "^2.18.3",
     "react-navigation-redux-helpers": "^2.0.9",
     "react-navigation-tabs": "0.8.4",

yarn.lock

@@ -7771,10 +7771,9 @@ react-native-vector-icons@^4.6.0:
     prop-types "^15.5.10"
     yargs "^8.0.2"
 
-react-native-webview@^5.0.0:
+"react-native-webview@git://github.com/zulip/react-native-webview#49aca8206":
   version "5.12.1"
-  resolved "https://registry.yarnpkg.com/react-native-webview/-/react-native-webview-5.12.1.tgz#5e2b124e9087d64fc40040d911c10ee5744b5d4d"
-  integrity sha512-pFYzyNUG+k7Jk2a0Z3S1+OL9qtp0VQxVP08d1ume/O6l1Xibi0K0hRZms7zPUHqQc2uWEfjZ0FOa17MIN7vruw==
+  resolved "git://github.com/zulip/react-native-webview#49aca8206f0f05dc17d7bafc96a2886dadec32b3"
   dependencies:
     escape-string-regexp "1.0.5"
     invariant "2.2.4"