Fix documentation typos in aws/config (#3417)

I stumbled upon a typo in the example code of
`EC2MetadataDisableTimeoutOverride`, and while at it, also fixed 2 more
typos here.

aws/config.go

@@ -138,7 +138,7 @@ type Config struct {
 	// `ExpectContinueTimeout` for information on adjusting the continue wait
 	// timeout. https://golang.org/pkg/net/http/#Transport
 	//
-	// You should use this flag to disble 100-Continue if you experience issues
+	// You should use this flag to disable 100-Continue if you experience issues
 	// with proxies or third party S3 compatible services.
 	S3Disable100Continue *bool
 
@@ -183,7 +183,7 @@ type Config struct {
 	//
 	// Example:
 	//    sess := session.Must(session.NewSession(aws.NewConfig()
-	//       .WithEC2MetadataDiableTimeoutOverride(true)))
+	//       .WithEC2MetadataDisableTimeoutOverride(true)))
 	//
 	//    svc := s3.New(sess)
 	//
@@ -194,7 +194,7 @@ type Config struct {
 	// both IPv4 and IPv6 addressing.
 	//
 	// Setting this for a service which does not support dual stack will fail
-	// to make requets. It is not recommended to set this value on the session
+	// to make requests. It is not recommended to set this value on the session
 	// as it will apply to all service clients created with the session. Even
 	// services which don't support dual stack endpoints.
 	//