redirect routing for prototype (#1030)

Fixes #1019.

Test plan: Loading the prototype works, as does clicking through to different prototype pages.

“Running `git grep -F '/prototypes/'` returns no results; before this commit, it yielded 2 results.”

src/homepage/PrototypesPage.js

@@ -26,7 +26,7 @@ export default function makePrototypesPage(
           <ul>
             {registry.map((x) => (
               <li key={stringify(x)}>
-                <Link to={`/prototypes/${x.repoId.owner}/${x.repoId.name}/`}>
+                <Link to={`/prototype/${x.repoId.owner}/${x.repoId.name}/`}>
                   {`${x.repoId.owner}/${x.repoId.name}`}
                 </Link>
               </li>

src/homepage/routeData.js

@@ -48,7 +48,7 @@ function makeRouteData(registry /*: RepoIdRegistry */) /*: RouteData */ {
       navTitle: "Prototype",
     },
     ...registry.map((entry) => ({
-      path: `/prototypes/${entry.repoId.owner}/${entry.repoId.name}/`,
+      path: `/prototype/${entry.repoId.owner}/${entry.repoId.name}/`,
       contents: {
         type: "PAGE",
         component: () => require("./ProjectPage").default(entry.repoId),