rectify 'a invalid version' to 'an invalid version'
rectify 'a invalid version' to 'an invalid version'

Change-Id: I854134736ce80cb27701afff508a6f7342a61d64

openstack/swift,tipabu/swift,swiftstack/swift,openstack/swift,swiftstack/swift,tipabu/swift,tipabu/swift,tipabu/swift,swiftstack/swift,openstack/swift,openstack/swift