Traivs: Add Xcode 9.4 and Linux 4.2 snap

Test builds on more platforms.

Author: helje5

.travis.yml

@@ -13,10 +13,16 @@ matrix:
           dist: trusty
           env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-4.1-release/ubuntu1404/swift-4.1-RELEASE/swift-4.1-RELEASE-ubuntu14.04.tar.gz"
           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"
+          sudo: required
         - os:   osx
           osx_image: xcode9
         - os:   osx
           osx_image: xcode9.3
+        - os:   osx
+          osx_image: xcode9.4
 
 
 before_install:
@@ -31,4 +37,3 @@ script:
     - export PATH="${SWIFTENV_ROOT}/bin:${SWIFTENV_ROOT}/shims:$PATH"
     - swift build -c release
     - swift build -c debug
-