Update Travis versions, add 5.2 builds

... also Xcode 11.4.

Author: helje5

.travis.yml

@@ -7,14 +7,20 @@ matrix:
     include:
         - os:   Linux
           dist: trusty
-          env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-5.0.2-release/ubuntu1404/swift-5.0.2-RELEASE/swift-5.0.2-RELEASE-ubuntu14.04.tar.gz"
+          env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-5.0.3-release/ubuntu1404/swift-5.0.3-RELEASE/swift-5.0.3-RELEASE-ubuntu14.04.tar.gz"
           sudo: required
         - os:   Linux
           dist: trusty
-          env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-5.1.3-release/ubuntu1404/swift-5.1.3-RELEASE/swift-5.1.3-RELEASE-ubuntu14.04.tar.gz"
+          env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-5.1.5-release/ubuntu1404/swift-5.1.5-RELEASE/swift-5.1.5-RELEASE-ubuntu14.04.tar.gz"
+          sudo: required
+        - os:   Linux
+          dist: xenial
+          env:  SWIFT_SNAPSHOT_NAME="https://swift.org/builds/swift-5.2.4-release/ubuntu1604/swift-5.2.4-RELEASE/swift-5.2.4-RELEASE-ubuntu16.04.tar.gz"
           sudo: required
         - os:   osx
           osx_image: xcode11
+        - os:   osx
+          osx_image: xcode11.4
 
 before_install:
     - ./.travis.d/before-install.sh