Update CHANGELOG.md

Merge pull request OmniSharp#1176 from rchande/version30changelog

Change log updates

Merge pull request OmniSharp#1175 from OmniSharp/masterToCodeAnalysis29

Master to code analysis29

Merge pull request OmniSharp#1174 from rchande/cs7.3

Allow specifying C# 7.3

Merge pull request OmniSharp#1160 from DustinCampbell/dont-over-notif…

…y-files

Ensure that we don't subscribe the same file-watcher callback multiple times

Merge pull request OmniSharp#1107 from rchande/fixDuplicateDiagnostics

Disable cake diagnostics endpoint for requests that don't specify a file

Merge pull request OmniSharp#1102 from OmniSharp/rchande-patch-1

Add more changes

Merge pull request OmniSharp#1064 from akshita31/space_after_c

Retain single leading space when appending string in TypeLookUp

Update CHANGELOG.md

Update CHANGELOG.md for 1.27.2