[SfpBase] Fix key name typo in docstring (#99)

Fix key name typo: "mominal_bit_rate" -> "nominal_bit_rate"

Author: jleveque

sonic_platform_base/sfp_base.py

@@ -35,7 +35,7 @@ def get_transceiver_info(self):
         ext_identifier             |1*255VCHAR     |extend identifier
         ext_rateselect_compliance  |1*255VCHAR     |extended rateSelect compliance
         cable_length               |INT            |cable length in m
-        mominal_bit_rate           |INT            |nominal bit rate by 100Mbs
+        nominal_bit_rate           |INT            |nominal bit rate by 100Mbs
         specification_compliance   |1*255VCHAR     |specification compliance
         vendor_date                |1*255VCHAR     |vendor date
         vendor_oui                 |1*255VCHAR     |vendor OUI