Updated 0.28.0 release date in changelog (#410)

Also update version string in README.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 930a340..73a4854 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-#### 0.28.0 - 2018-01-12
+#### 0.28.0 - 2018-01-19
 
    * BREAKING CHANGE: The signature of `MultiMap`'s `update` stub has changed
      from `V update(K key, C update(C value), {C ifAbsent()})` to
diff --git a/README.md b/README.md
index e051d3c..1b9fb26 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@
 We recommend the following version constraint:
 
     dependencies:
-      quiver: '>=0.27.0 <0.28.0'
+      quiver: '>=0.28.0 <0.29.0'
 
 # Main Libraries