Fix -plugin command line argument syntax for clang -cc1 change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@92780 91177308-0d34-0410-b5e6-96231b3b80d8

examples/PrintFunctionNames/README.txt

@@ -6,5 +6,5 @@ TOOL_NO_EXPORT in the tools/clang Makefile).
 
 Once the plugin is built, you can run it using:
 --
-$ clang -cc1 -load path/to/PrintFunctionNames.so -plugin=print-fns some-input-file.c
+$ clang -cc1 -load path/to/PrintFunctionNames.so -plugin print-fns some-input-file.c
 --