doc: rename namespace from google (deprecated) to gflags (default)

doc/gflags.html

@@ -269,7 +269,7 @@ the getopt library, but has much less overhead to use.  In fact, it's
 just a single function call:</p>
 
 <pre>
-   google::ParseCommandLineFlags(&argc, &argv, true);
+   gflags::ParseCommandLineFlags(&argc, &argv, true);
 </pre>
 
 <p>Usually, this code is at the beginning of <code>main()</code>.
@@ -529,8 +529,8 @@ access parts of <code>argv</code> outside main, including the program
 name (<code>argv[0]</code>).</p>
 
 <p>For more information about these routines, and other useful helper
-methods such as <code>google::SetUsageMessage()</code> and
-<code>google::SetVersionString</code>, see <code>gflags.h</code>.</p>
+methods such as <code>gflags::SetUsageMessage()</code> and
+<code>gflags::SetVersionString</code>, see <code>gflags.h</code>.</p>
 
 
 <h2> <A name="misc">Miscellaneous Notes</code> </h2>