Fix a typo in gn help.

tools/gn/command_help.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <iostream>
 
 #include "base/command_line.h"
 #include "tools/gn/args.h"
 #include "tools/gn/commands.h"
@@ skipping 53 matching lines @@
   OutputString("\nOther help topics:\n");
   PrintShortHelp("all: Print all the help at once");
   PrintShortHelp("buildargs: How build arguments work.");
   PrintShortHelp("dotfile: Info about the toplevel .gn file.");
   PrintShortHelp("execution: Build graph and execution overview.");
   PrintShortHelp("grammar: Language and grammar for GN build files.");
   PrintShortHelp(
       "input_conversion: Processing input from exec_script and read_file.");
   PrintShortHelp("label_pattern: Matching more than one label.");
   PrintShortHelp("labels: About labels.");
-  PrintShortHelp("ninja_rules: How Ninja build rules and named.");
+  PrintShortHelp("ninja_rules: How Ninja build rules are named.");
   PrintShortHelp("nogncheck: Annotating includes for checking.");
   PrintShortHelp("runtime_deps: How runtime dependency computation works.");
   PrintShortHelp("source_expansion: Map sources to outputs for scripts.");
   PrintShortHelp("switches: Show available command-line switches.");
 }
 
 void PrintSwitchHelp() {
   const base::CommandLine* cmdline = base::CommandLine::ForCurrentProcess();
   bool use_markdown = cmdline->HasSwitch(switches::kMarkdown);
 
@@ skipping 195 matching lines @@
     OutputString("Run `gn help` for a list of available topics.\n",
                  DECORATION_NONE);
   } else {
     OutputString("Did you mean `gn help " + suggestion.as_string() + "`?\n",
                  DECORATION_NONE);
   }
   return 1;
 }
 
 }  // namespace commands