Fix misspelling of environment throughout libc++

llvm-svn: 302600
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 78046e462417425daae02ddc7a472df117dfd05e
diff --git a/docs/TestingLibcxx.rst b/docs/TestingLibcxx.rst
index e429276..5c48ebe 100644
--- a/docs/TestingLibcxx.rst
+++ b/docs/TestingLibcxx.rst
@@ -119,7 +119,7 @@
 .. option:: libcxx_site_config=<path/to/lit.site.cfg>
 
   Specify the site configuration to use when running the tests.  This option
-  overrides the enviroment variable LIBCXX_SITE_CONFIG.
+  overrides the environment variable LIBCXX_SITE_CONFIG.
 
 .. option:: cxx_headers=<path/to/headers>