Travis: built on 4.2.1 release

... and Xcode 10/10.1

Author: helje5

.travis.yml

@@ -15,14 +15,18 @@ matrix:
  sudo: required
  - os: Linux
  dist: trusty
- env: SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-4.2-branch/ubuntu1404/swift-4.2-DEVELOPMENT-SNAPSHOT-2018-07-24-a/swift-4.2-DEVELOPMENT-SNAPSHOT-2018-07-24-a-ubuntu14.04.tar.gz"
+ env: SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-4.2.1-release/ubuntu1404/swift-4.2.1-RELEASE/swift-4.2.1-RELEASE-ubuntu14.04.tar.gz"
  sudo: required
  - os: osx
  osx_image: xcode9
  - os: osx
  osx_image: xcode9.3
  - os: osx
  osx_image: xcode9.4
+ - os: osx
+ osx_image: xcode10
+ - os: osx
+ osx_image: xcode10.1
 
 
 before_install: