Fix some whitespace around the cpplint error

Author: peternewman

Makefile.am

@@ -261,5 +261,5 @@ cpplint: Makefile.am
 if FOUND_CPPLINT
 	cpplint --filter=$(CPP_LINT_FILTER) $(CPP_LINT_FILES)
 else
-  $(error cpplint not found. Install forked cpplint (e.g. via pip for the latest version) and re-run configure.)
+	$(error cpplint not found. Install the forked cpplint (e.g. via pip for the latest version) and re-run configure.)
 endif