Fix grammar-o.

llvm-svn: 223265
diff --git a/llvm/docs/CMake.rst b/llvm/docs/CMake.rst
index 653fa16..47cb2f3 100644
--- a/llvm/docs/CMake.rst
+++ b/llvm/docs/CMake.rst
@@ -234,7 +234,7 @@
   Enable all compiler warnings. Defaults to ON.
 
 **LLVM_ENABLE_PEDANTIC**:BOOL
-  Enable pedantic mode. This disable compiler specific extensions, is
+  Enable pedantic mode. This disables compiler specific extensions, if
   possible. Defaults to ON.
 
 **LLVM_ENABLE_WERROR**:BOOL