Fix typo on splash page

Why these changes are being introduced:

The last update to the docs added a typo that I missed at the time,
but will make me flip a table every time I see it.

Relevant ticket(s):

N/A.

How this addresses that need:

This fixes the typo.

Side effects of this change:

None.

app/views/static/index.html.erb

@@ -10,7 +10,7 @@
       <p>We currently provide searching of records in MIT Libraries catalog, DSpace@MIT, and MIT ArchivesSpace.</p>
 
       <p>Access is via a <a href="https://graphql.org">GraphQL</a> endpoint by posting to <%= link_to(graphql_url) %>.
-        We recommend starting by exploring our <a href="/playground">interactive GraphQL playground.</a>, or you can
+        We recommend starting by exploring our <a href="/playground">interactive GraphQL playground</a>, or you can
         look through our <a href="https://mitlibraries.github.io/timdex/">developer documentation</a> for how-to guides,
         API reference, and more.