doc: update DWARF version

Change-Id: I0d02e5e44053f02fee3d84c782995ea4ce209a80
Reviewed-on: https://go-review.googlesource.com/62070Reviewed-by: Heschi Kreinick <heschi@google.com>

doc/debugging_with_gdb.html

@@ -31,8 +31,8 @@ In time, a more Go-centric debugging architecture may be required.
 
 <p>
 When you compile and link your Go programs with the <code>gc</code> toolchain
-on Linux, Mac OS X, FreeBSD or NetBSD, the resulting binaries contain DWARFv3
-debugging information that recent versions (&gt;7.1) of the GDB debugger can
+on Linux, Mac OS X, FreeBSD or NetBSD, the resulting binaries contain DWARFv4
+debugging information that recent versions (&gt;7.5) of the GDB debugger can
 use to inspect a live process or a core dump.
 </p>