.gitignore sms.db

When running osmo-msc in osmo-ttcn3-hacks/msc, it will leave behind an
sms.db. Ignore it.

Change-Id: Ib4c66a9861f92293520c4c38a50d4d51f3cf2a77
diff --git a/.gitignore b/.gitignore
index b247c04..9d48551 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,4 @@
 *.netcat.stderr
 *.d
 *.merged
+sms.db