Properly set the lower bound for packages' dependencies on source_maps.

pkg/observe/CHANGELOG.md

Index: pkg/observe/CHANGELOG.md
diff --git a/pkg/observe/CHANGELOG.md b/pkg/observe/CHANGELOG.md
index c9cded8059519b3a905ca8b4d0f554d82428e973..2966b03f07ec7b1e04ca7ecb190e7bff444a3640 100644
--- a/pkg/observe/CHANGELOG.md
+++ b/pkg/observe/CHANGELOG.md
@@ -3,6 +3,10 @@
 This file contains highlights of what changes on each version of the observe
 package.
 
+#### Pub version 0.11.0+4
+  * Raise the lower bound on the source_maps constraint to exclude incompatible
+    versions.
+
 #### Pub version 0.11.0+3
   * Widen the constraint on source_maps.