THRIFT-4019: Dart Makefiles should also clean pubspec.lock
Client: Dart
Patch: Mark Erickson <merickson@apache.org>

This closes #1150
diff --git a/lib/dart/Makefile.am b/lib/dart/Makefile.am
index a6e4556..910db50 100644
--- a/lib/dart/Makefile.am
+++ b/lib/dart/Makefile.am
@@ -24,5 +24,6 @@
 	$(RM) -r .pub
 	find . -type d -name "packages" | xargs $(RM) -r
 	find . -type f -name ".packages" | xargs $(RM)
+	find . -type f -name "pubspec.lock" | xargs $(RM)
 
 check-local: all