Typo fix

README.md

@@ -180,7 +180,7 @@ their customers' accounts.
 Proxy url for proxying requests to amazon sts service api. This needs to be  set up independently from global http_proxy parameter
 for the use case in which requests to kinesis api are going via kinesis vpc endpoint but requests to sts api have to go via http proxy. 
 It should be added to assume_role_credentials configuration stanza in the next format:
-    sts_http_proxy http://[useriname:password]@hostname:port
+    sts_http_proxy http://[username:password]@hostname:port
 
 ### instance_profile_credentials