doc/debugging_with_gdb: fix the link of delve

The repository of delve has already switched from the personal
account github.com/derekparker/delve to the organization account
github.com/go-delve/delve. According to go-delve/delve#1456.

doc/debugging_with_gdb.html

@@ -18,13 +18,13 @@
 </p>
 <p>
 Note that 
-<a href="https://github.com/derekparker/delve">Delve</a> is a better 
+<a href="https://github.com/go-delve/delve">Delve</a> is a better
 alternative to GDB when debugging Go programs built with the standard
 toolchain. It understands the Go runtime, data structures, and
 expressions better than GDB. Delve currently supports Linux, OSX,
 and Windows on <code>amd64</code>.
 For the most up-to-date list of supported platforms, please see
-<a href="https://github.com/derekparker/delve/tree/master/Documentation/installation">
+<a href="https://github.com/go-delve/delve/tree/master/Documentation/installation">
  the Delve documentation</a>.
 </p>
 </i>