Revert analyzer Dart language version to 2.12

Change-Id: I2076c6134f8da11ef78db96433241e2eea779a15
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/204700
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
diff --git a/.dart_tool/package_config.json b/.dart_tool/package_config.json
index 44baa91..efcb595 100644
--- a/.dart_tool/package_config.json
+++ b/.dart_tool/package_config.json
@@ -82,7 +82,7 @@
       "name": "analyzer",
       "rootUri": "../pkg/analyzer",
       "packageUri": "lib/",
-      "languageVersion": "2.13"
+      "languageVersion": "2.12"
     },
     {
       "name": "analyzer_cli",
diff --git a/pkg/analyzer/pubspec.yaml b/pkg/analyzer/pubspec.yaml
index 529d76a..b3cbff8 100644
--- a/pkg/analyzer/pubspec.yaml
+++ b/pkg/analyzer/pubspec.yaml
@@ -4,7 +4,7 @@
 homepage: https://github.com/dart-lang/sdk/tree/master/pkg/analyzer
 
 environment:
-  sdk: '>=2.13.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   _fe_analyzer_shared: ^22.0.0