Roll coveralls back to latest.  (Fix #10.)

tool/travis.sh

diff --git a/tool/travis.sh b/tool/travis.sh
index 5ac7ef5..9d9a8a4 100755
--- a/tool/travis.sh
+++ b/tool/travis.sh
@@ -18,7 +18,7 @@
 
 # Install dart_coveralls; gather and send coverage data.
 if [ "$COVERALLS_TOKEN" ]; then
-  pub global activate dart_coveralls 0.1.11
+  pub global activate dart_coveralls
   pub global run dart_coveralls report \
     --token $COVERALLS_TOKEN \
     --retry 2 \