Explicitly choose Mono 4.0.5 - avoids future problems related to aspnet/External#48   - e.g. when Travis updates default Mono version in `csharp` bundle
Explicitly choose Mono 4.0.5
- avoids future problems related to aspnet/External#48
  - e.g. when Travis updates default Mono version in `csharp` bundle

aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore,aspnet/AspNetCore