Bump min SDK to workaround broken analyzer (dart-lang/stream_transform#112)

There is a broken version of `package:analyzer` that causes issues on
travis for the `2.6.0` SDK. There is relatively little need to maintain
support for an SDK that old, so bump the minimum rather than pin
analyzer and be unable to pick up newer versions.

https://github.com/dart-lang/sdk/issues/42888

Fix formatting in changelog.

pkgs/stream_transform/.travis.yml

diff --git a/pkgs/stream_transform/.travis.yml b/pkgs/stream_transform/.travis.yml
index 596c0c6..24eb0d7 100644
--- a/pkgs/stream_transform/.travis.yml
+++ b/pkgs/stream_transform/.travis.yml
@@ -3,7 +3,7 @@
   only: [master]
 dart:
   - dev
-  - 2.6.0
+  - 2.7.0
 cache:
   directories:
     - $HOME/.pub-cache
@@ -18,6 +18,6 @@
     - dart: dev
       dart_task:
         dartanalyzer: --fatal-warnings --fatal-infos .
-    - dart: 2.6.0
+    - dart: 2.7.0
       dart_task:
         dartanalyzer: --fatal-warnings .

pkgs/stream_transform/CHANGELOG.md

diff --git a/pkgs/stream_transform/CHANGELOG.md b/pkgs/stream_transform/CHANGELOG.md
index 73fc368..268bf35 100644
--- a/pkgs/stream_transform/CHANGELOG.md
+++ b/pkgs/stream_transform/CHANGELOG.md
@@ -1,6 +1,7 @@
 ## 1.2.1-dev
 
-* Improve tests of `switchMap` and improve documentation with links and clarification.
+- Improve tests of `switchMap` and improve documentation with links and
+  clarification.
 
 ## 1.2.0
 

pkgs/stream_transform/pubspec.yaml

diff --git a/pkgs/stream_transform/pubspec.yaml b/pkgs/stream_transform/pubspec.yaml
index c566c16..5da90b1 100644
--- a/pkgs/stream_transform/pubspec.yaml
+++ b/pkgs/stream_transform/pubspec.yaml
@@ -4,7 +4,7 @@
 version: 1.2.1-dev
 
 environment:
-  sdk: ">=2.6.0 <3.0.0"
+  sdk: ">=2.7.0 <3.0.0"
 
 dev_dependencies:
   async: ^2.0.0