Corrected the bug: issue 101

in mpl_server.py: get_fig_by_id(): fig_id -> str(fig_id)

mpl_server.py

@@ -330,10 +330,10 @@ class MplServer(socketserver.TCPServer):
         fig = self._figures.get(fig_id,None)
         if fig is None:
             if debug:
-                print(WARN + "The figure ID: " + fig_id + " does not exist.")
+                print(WARN + "The figure ID: " + str(fig_id) + " does not exist.")
             return Status(False, "The figure ID: "
-                          + fig_id + " does not exist.")
+                          + str(fig_id) + " does not exist.")
         elif isinstance(fig, MplFig):
             if debug:
-                print('Figure ', fig_id, ' found in database')
+                print('Figure ' + str(fig_id) + ' found in database')
             return fig