fix grammatical error

Author: nickdesaulniers

libc/docs/dev/code_style.rst

@@ -238,7 +238,7 @@ level languages like Assembly, such as:
 While it's not impossible to have Assembly code that correctly provides all of
 the above, we do not wish to maintain such Assembly sources in llvm-libc.
 
-That said, there a few functions provided by llvm-libc that are impossible
+That said, there are a few functions provided by llvm-libc that are impossible
 to reliably implement in C++ for all compilers supported for building
 llvm-libc.