Update Dart.gitignore
Update Dart.gitignore

Removed space from end of line which prevented the `pubspec.lock` from being ignored.
chhsieh/helloworld,bruennijs/ise.cppworkshop,szymanskirafal/gitignore,bruennijs/ise.cppworkshop,chhsieh/gitTest_1,szymanskirafal/gitignore,szymanskirafal/gitignore,bruennijs/ise.cppworkshop