Require at least analyzer 0.27.3-alpha.1

dart-lang/sdk#25822

Author: kevmoo

pubspec.yaml

@@ -6,7 +6,7 @@ homepage: https://github.com/dart-lang/source_gen
 environment:
   sdk: '>=1.12.0 <2.0.0'
 dependencies:
-  analyzer: '^0.27.1'
+  analyzer: '^0.27.3-alpha.1'
   args: '>=0.12.2+3 <0.14.0'
   cli_util: ^0.0.1
   dart_style: '>=0.1.7 <0.3.0'