Fix a small grammar problem.

pep-0552.rst

@@ -24,7 +24,7 @@ Rationale
 A `reproducible build`_ is one where the same byte-for-byte output is generated
 every time the same sources are built—even across different machines (naturally
 subject to the requirement that they have rather similar environments
-setup). Reproducibility is important for security. It is also a key concept in
+set up). Reproducibility is important for security. It is also a key concept in
 content-based build systems such as Bazel_, which are most effective when the
 output files’ contents are a deterministic function of the input files’
 contents.