CI updates: use xcode 10.3 (instead of 10.2), additionally test/benchmark using xcode 11.3

Author: tsolomko

.travis.yml

@@ -3,12 +3,21 @@ jobs:
     - stage: test
       language: swift
       os: osx
-      osx_image: xcode10.2
+      osx_image: xcode10.3
       script:
       - swift build
       - swift test --filter BitByteDataTests
       - swift build -c release # Check Release build just in case.
-    - language: generic
+    - stage: test
+      language: swift
+      os: osx
+      osx_image: xcode11.3
+      script:
+      - swift build
+      - swift test --filter BitByteDataTests
+      - swift build -c release # Check Release build just in case.
+    - stage: test
+      language: generic
       os: linux
       dist: xenial
       install:
@@ -21,7 +30,14 @@ jobs:
       if: NOT (tag IS present)
       language: swift
       os: osx
-      osx_image: xcode10.2
+      osx_image: xcode10.3
+      script:
+      - ./benchmarks.py run
+    - stage: benchmark
+      if: NOT (tag IS present)
+      language: swift
+      os: osx
+      osx_image: xcode11.3
       script:
       - ./benchmarks.py run
     - stage: benchmark
@@ -37,7 +53,7 @@ jobs:
       if: tag IS present
       language: generic
       os: osx
-      osx_image: xcode10.2
+      osx_image: xcode10.3
       env:
         secure: fmKQgrPRx2iisNPzxDhOTfXPsnQMJxDgIMItVNjl1AKByraOpiDAGVESySvy+vwQqITCB/BfvdkW7smAPcvFJxIPRx1v4J0VY9kGHdnafMw35XY0Vj9soYkzNS4zrUebxY2gWkGM6Q6dgLOGT/9MSEyWqXBTtVz9sLwA7yr3ZI72yZDbcSz3XGa1fFZRVfwv3I+bmuozG7dq7tyqcSKgRZnHg1VvaRdxcaGqSGSUsNu0YLzmNedujNcU+gTXcxMdrXA1eaheHc2pwNA0TDf3KkefJpaVMXrA/Un8e9MaJ1lMnPlIiEI3dPTuogtQY7p59vgulBNBPEJovTHI0jCaNyLUkTkHgGcUuOwHqwUIKZCEiiqM1j12sdLo4O2tAdNaNHDtd8D3bCakrdJxXlUWVfjrCwvBB555gd0drRirQgYX+5gGFwnTQE8tOcjK4qUvJaOAouHsnm/DmW+fLJPX76KoU6QOtGJt6PQ92yBgKRhaSg/sQ28WPuCmF2p7BuUSuULxcM2LU5eA5aFxayoZvR2E9uvfFxnFh01iV6clcZo25U03AuxJmuI7Mhl83amj8bm5CRBbuRw5sIljXfBujFUel+kz/HXalS7lStqH9iPyiQvh24WkPzHKNQdjRI7v3kyrVSXJ3Xl6+fopXqr/25MwqD4bt57QgglJ2IQtnLM=
       addons: