Improve CHANGELOG formatting
Improve CHANGELOG formatting

Lack of 2nd newline after CHANGED results in the CHANGELOG bot
creating entries that looked odd in GitHub.

This closes #1503

dipinhora/ponyc,sgebbie/ponyc,cquinn/ponyc,Perelandric/ponyc,boemmels/ponyc,jemc/ponyc,jupvfranco/ponyc,kulibali/ponyc,sgebbie/ponyc,CausalityLtd/ponyc,sgebbie/ponyc,dipinhora/ponyc,jupvfranco/ponyc,jemc/ponyc,jupvfranco/ponyc,dipinhora/ponyc,kulibali/ponyc,cquinn/ponyc,boemmels/ponyc,Theodus/ponyc,Perelandric/ponyc,mkfifo/ponyc,sgebbie/ponyc,Theodus/ponyc,kulibali/ponyc,ponylang/ponyc,Theodus/ponyc,ponylang/ponyc,Praetonus/ponyc,Perelandric/ponyc,Praetonus/ponyc,Perelandric/ponyc,CausalityLtd/ponyc,jupvfranco/ponyc,boemmels/ponyc,Praetonus/ponyc,cquinn/ponyc,sgebbie/ponyc,mkfifo/ponyc,Theodus/ponyc,cquinn/ponyc,CausalityLtd/ponyc,mkfifo/ponyc,mkfifo/ponyc,jupvfranco/ponyc,Theodus/ponyc,jemc/ponyc,Perelandric/ponyc,ponylang/ponyc,boemmels/ponyc,boemmels/ponyc,kulibali/ponyc,mkfifo/ponyc,Praetonus/ponyc