add path dependency (see dart-lang/sdk#25710)

Author: kasperpeulen

pubspec.yaml

@@ -5,8 +5,11 @@ homepage: https://github.com/kasperpeulen/kp_directory.dart
 version: 0.0.1
 environment:
   sdk: '>=1.13.0 <2.0.0'
+dependencies:
+  path: '^1.3.9'
 dev_dependencies:
   test: ^0.12.6+1
   grinder: ^0.8.0+1
   coverage: ^0.7.2
   dart_dev: ^1.0.5
+