build: Add .version to EXTRA_DIST

This is required to make distcheck work and apparently that's
the "good way" to do it.

See http://comments.gmane.org/gmane.comp.lib.gnulib.bugs/27780

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/Makefile.am b/Makefile.am
index a77bd8f..717d3db 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -13,7 +13,7 @@
 dist-hook:
 	echo $(VERSION) > $(distdir)/.tarball-version
 
-EXTRA_DIST = git-version-gen
+EXTRA_DIST = git-version-gen .version
 
 if HAVE_DOXYGEN