Fix typo

Author: alisinabh

README.md

@@ -77,7 +77,7 @@ config :ethers,
   default_signer: nil, # Defaults to: nil, see Ethers.Signer for more info
   default_signer_opts: [], # Defaults to: []
   default_gas_margin: 11000, # Precision is 0.01% (11000 = 110%)
-  default_mdefault_max_fee_per_gas_margin: 12000 #Precision is 0.01% (12000 = 120%)
+  default_max_fee_per_gas_margin: 12000 #Precision is 0.01% (12000 = 120%)
 
 # If using Ethereumex, you can specify a default JSON-RPC server url here for all requests.
 config :ethereumex, url: "[URL_HERE]"