aws/signer/v4: Correct wording for v4 signer's docs
aws/signer/v4: Correct wording for v4 signer's docs


radeksimko/aws-sdk-go,calgaryscientific/aws-sdk-go,agworld/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,yxd-hde/aws-sdk-go,radeksimko/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,radeksimko/aws-sdk-go,calgaryscientific/aws-sdk-go,agworld/aws-sdk-go,agworld/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,jasdel/aws-sdk-go,yxd-hde/aws-sdk-go,aws/aws-sdk-go