Update experimental_mixed_language_library.bzl

Co-authored-by: Matt Robinson <[email protected]>

apple/internal/experimental_mixed_language_library.bzl

@@ -209,7 +209,7 @@ def experimental_mixed_language_library(
     This is an experimental macro that supports compiling mixed Objective-C and
     Swift source files into a static library.
 
-    Due to build performance reason, in general it's not recommended to
+    Due to build performance reasons, in general it's not recommended to
     have mixed Objective-C and Swift modules, but it isn't uncommon to see
     mixed language modules in some codebases. This macro is meant to make
     it easier to migrate codebases with mixed language modules to Bazel without