[release] Prepare changelog for 2.1.0-dev.7.0

TBR=whesse@google.com

Change-Id: I08a4b0b504dbaae589b07c48db3d81a7d579e69b
Reviewed-on: https://dart-review.googlesource.com/c/79100
Reviewed-by: Alexander Thomas <athom@google.com>

CHANGELOG.md

@@ -4,6 +4,20 @@
 
 ### Language
 
+### Core library changes
+
+### Dart VM
+
+### Tool Changes
+
+#### Pub
+
+#### Other Tools
+
+## 2.1.0-dev.7.0
+
+### Language
+
 *   Fixed a bug (issue [32014](http://dartbug.com/32014)) that caused invalid
     implementations of the interface of a class to not be reported in some cases.
     For instance, the following code would not produce a compile-time error:
@@ -53,14 +67,6 @@
 *   Made `Uri` parsing more permissive about `[` and `]` occurring
     in the path, query or fragment, and `#` occurring in fragment.
 
-### Dart VM
-
-### Tool Changes
-
-#### Pub
-
-#### Other Tools
-
 ## 2.1.0-dev.6.0
 
 ## 2.1.0-dev.5.0