Drop mono 4.2.3 since it can't build net46

bording · bording · commit 332f4df4254a · 2017-04-01T16:21:55.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -4,7 +4,6 @@
 language: csharp
 mono:
  - latest
- - 4.2.3
 
 os:
  - osx

-Original file line number
+Diff line change
 language: csharp
 mono:
  - latest
 - - 4.2.3
 os:
  - osx