Testing last SDKs on travis

Add firefox and a xvfb startup pause
Run one test at a time
diff --git a/.travis.yml b/.travis.yml
index 2576e2a..0ceff2e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,16 +3,17 @@
 dart:
   - stable
   - dev
-  - 1.16.0
-  - 1.15.0
-  - 1.14.2
-  - 1.13.2
-  - 1.12.2
+  - 1.19.0
+  - 1.18.1
+  - 1.17.1
 cache:
   directories:
     - $HOME/.pub-cache
 with_content_shell: true
-before_install:
+addons:
+  firefox: "latest"
+before_script:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"
+  - 't=0; until (xdpyinfo -display :99 &> /dev/null || test $t -gt 10); do sleep 1; let t=$t+1; done'
 script: ./tool/travis.sh
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1e541a5..0be6ff2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.6.6
+
+* Bump minimum supported Dart SDK to `>=1.13.2`.
+
 ## 0.6.5+3
 
 * Improve the documentation of `logRequests()`.
diff --git a/pubspec.yaml b/pubspec.yaml
index 2376077..8650a85 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,10 +1,10 @@
 name: shelf
-version: 0.6.5+3
+version: 0.6.6-dev
 author: Dart Team <misc@dartlang.org>
 description: Web Server Middleware for Dart
 homepage: https://github.com/dart-lang/shelf
 environment:
-  sdk: '>=1.12.0 <2.0.0'
+  sdk: '>=1.13.2 <2.0.0'
 dependencies:
   async: '^1.10.0'
   http_parser: '>=1.0.0 <4.0.0'
diff --git a/tool/travis.sh b/tool/travis.sh
index a1d0861..6604af3 100755
--- a/tool/travis.sh
+++ b/tool/travis.sh
@@ -3,7 +3,7 @@
 # Fast fail the script on failures.
 set -e
 
-pub run test -p vm,content-shell,firefox
+pub run test -p vm,content-shell,firefox -j 1
 
 # Install dart_coveralls; gather and send coverage data.
 if [ "$COVERALLS_TOKEN" ] && [ "$TRAVIS_DART_VERSION" = "stable" ]; then