Adds pymysql to requirements.txt

Allows using a mysql database as peewee backend

Change-Id: If0c408d57f9d20d36a04e5cf8421a0a9f9c1d0b9
Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>
diff --git a/requirements.txt b/requirements.txt
index f6451e4..5665a39 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,4 +3,5 @@
 jsonschema==2.6.*
 six==1.11.*
 pyyaml==3.*
+pymysql
 git+https://osm.etsi.org/gerrit/osm/common.git#egg=osm-common