Makefile.am: generate missing .version file

Change-Id: Id0cd2debf9b2d120c6dec1e534eefc4fe0a4210f
diff --git a/.gitignore b/.gitignore
index c8b1d06..20c6470 100644
--- a/.gitignore
+++ b/.gitignore
@@ -42,8 +42,11 @@
 tests/testsuite
 tests/testsuite.log
 
-# ignore debian files
+# git-version-gen magic
 .tarball-version
+.version
+
+# ignore debian files
 debian/autoreconf.after
 debian/autoreconf.before
 debian/files