RegexGroup.cs - Array.Empty<int>() would not compile. Replaced with new int[] {}

https://github.com/dotnet/corefx/pull/229
InfiniteMatchTimeout wouldn't build in .NET 3.5
RegexGroup.cs - Array.Empty<int>() would not compile. Replaced with new int[] {}

https://github.com/dotnet/corefx/pull/229
InfiniteMatchTimeout wouldn't build in .NET 3.5
Merge branch 'CADbloke' of https://github.com/CADbloke/corefx into CADbloke
Merge branch 'CADbloke' of https://github.com/CADbloke/corefx