Minor docstring fix

Made docstring consistent with code wrt snclMapper option.

geomagio/edge/EdgeFactory.py

@@ -65,7 +65,7 @@ class EdgeFactory(TimeseriesFactory):
         all data written to edge (via raw input client) will be scaled
         by this integer prior to write; all data read from edge will be
         will be divided by this integer after read; default = 1000
-    snclMapper: {'default','legacy','iris'}
+    snclMapper: {'geomag','legacy'}
         a mapper of common channel names to SEED SNCL codes (that is,
         station, network, channel, location codes); default = legacy