Remove unused dependency on the path package.

BUG=
R=sigmund@google.com

Review-Url: https://codereview.chromium.org//2732253003 .
diff --git a/pubspec.yaml b/pubspec.yaml
index 6185512..c101271 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -4,7 +4,6 @@
 description: Library to programmatically manipulate source map files.
 homepage: http://github.com/dart-lang/source_maps
 dependencies:
-  path: ^1.2.0
   source_span: ^1.1.1
 environment:
   sdk: '>=1.8.0 <2.0.0'