update build instructions

.travis.yml

@@ -10,7 +10,7 @@ install:
 script:  
     # coverage run --source=pwman setup.py test
     # coverage run --omit=pwman/tests/*.py --source=pwman setup.py test
-    coverage run --omit="pwman/tests/*.py,pwman/ui/mac.py,pwman/ui/win.py,pwman/data/convertdb.py,pwman/data/nodes_multiple_approach.py,pwman/data/models.py" --source=pwman setup.py test
+    coverage run --omit="pwman/tests/*.py,pwman/ui/mac.py,pwman/ui/win.py,pwman/data/convertdb.py,pwman/data/nodes_multiple_approach.py,pwman/data/models.py,pwman/data/drivers/postgresql.py,pwman/data/drivers/mysql.py" --source=pwman setup.py test
 
 
 after_success: