Fix a number of outdated URLs across a number of markdown files

http -> https where appropriate
dartlang.org -> dart.dev
...and others

Change-Id: I996afdd63d0c743cbabf7d29ade9e36cc3536fe8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149340
Auto-Submit: Kevin Moore <kevmoo@google.com>
Reviewed-by: Michael Thomsen <mit@google.com>
Commit-Queue: Michael Thomsen <mit@google.com>

https://dart.googlesource.com/sdk/+/26c1dec7ae2980395f44e7cf8fc9a14755c9f60a
diff --git a/commits.json b/commits.json
index e45431f..1620367 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"c19459ab7d3f30c87a403aee6aadb483968c82ec",
   "external/github.com/flutter/flutter":"a1636b6fef2ebe7840ba6dc1b3f9d77095ef3b45",
-  "sdk":"1ad89b85a2ee82e42c3b522069208892f5e7a1e7"
+  "sdk":"26c1dec7ae2980395f44e7cf8fc9a14755c9f60a"
 }
\ No newline at end of file