Add Jonathan Schear as a maintainer (#950)

Trying to figure out why the release automation isn't publishing to BCR;
current theory is we're missing a maintainer with a Github username, or
the trailing comma in the maintainers list is a problem. Whatever the
case, add me 😄

Author: jschear

.bcr/metadata.template.json

@@ -5,6 +5,11 @@
       "email": "[email protected]",
       "name": "rules_ios Maintainers"
     },
+    {
+      "name": "Jonathan Schear",
+      "email": "[email protected]",
+      "github": "jschear"
+    }
   ],
   "repository": [
     "github:bazel-ios/rules_ios"