Merge pull request #2373 from rust-lang/prior-art-patch-1

Typo 2: Change exists to exist in template.md#prior-art [prior art RFC]

text/2333-prior-art.md

@@ -95,7 +95,7 @@ text to the RFC template before the section *Unresolved questions*:
 > A few examples of what this can include are:
 >
 > - For language, library, cargo, tools, and compiler proposals:
->   Does this feature exists in other programming languages and
+>   Does this feature exist in other programming languages and
 >   what experience have their community had?
 > - For community proposals: Is this done by some other community and what
 >   were their experiences with it?