Makefile: updated clean target to remove osm-imdocs related stuff

Change-Id: Iee2f440a0a3492de5373f6dc52e716c7f6b1ef24
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/Makefile b/Makefile
index 7c41b11..8256a67 100644
--- a/Makefile
+++ b/Makefile
@@ -108,4 +108,4 @@
 	$(Q)cp -n ~/.m2/settings.xml{,.orig} ; wget -q -O - https://raw.githubusercontent.com/opendaylight/odlparent/master/settings.xml > ~/.m2/settings.xml
 
 clean:
-	$(Q)rm -rf dist osm_im.egg-info deb deb_dist *.gz yang2swagger $(OUT_DIR) $(TREES_DIR)
+	$(Q)rm -rf dist osm_im.egg-info deb deb_dist *.gz osm-imdocs* yang2swagger $(OUT_DIR) $(TREES_DIR)