osmo-mgw.spec.in: Add missing dependency to libosmotrau

Change-Id: I2d5f8b1d852079b8f82adb681d7e6b72a8358cf1
diff --git a/contrib/osmo-mgw.spec.in b/contrib/osmo-mgw.spec.in
index 0f96ed0..fc618da 100644
--- a/contrib/osmo-mgw.spec.in
+++ b/contrib/osmo-mgw.spec.in
@@ -35,7 +35,8 @@
 BuildRequires:  pkgconfig(libosmogsm) >= 1.0.0
 BuildRequires:  pkgconfig(libosmovty) >= 1.0.0
 BuildRequires:  pkgconfig(libosmocoding) >= 1.0.0
-BuildRequires:  pkgconfig(libosmoabis)
+BuildRequires:  pkgconfig(libosmoabis) >= 1.0.0
+BuildRequires:  pkgconfig(libosmotrau) >= 1.0.0
 %{?systemd_requires}
 
 %description