Update date in changelog. (#2926)

* Update changelog.

Author: sean-mcmanus

Extension/CHANGELOG.md

@@ -1,6 +1,6 @@
 # C/C++ for Visual Studio Code Change Log
 
-## Version 0.21.0-insiders2: December 13, 2018
+## Version 0.21.0-insiders2: December 17, 2018
 * Add documentation comments for hover, completion, and signature help. [#399](https://github.com/Microsoft/vscode-cpptools/issues/399)
 * Fix bugs when UTF-8 characters > 1 byte are used. [#1504](https://github.com/Microsoft/vscode-cpptools/issues/1504), [#1525](https://github.com/Microsoft/vscode-cpptools/issues/1525), [#2034](https://github.com/Microsoft/vscode-cpptools/issues/2034), [#2082](https://github.com/Microsoft/vscode-cpptools/issues/2082), [#2883](https://github.com/Microsoft/vscode-cpptools/issues/2883)
 * Fix some IntelliSense process crashes. [#1785](https://github.com/Microsoft/vscode-cpptools/issues/1785), [#2913](https://github.com/Microsoft/vscode-cpptools/issues/2913)
@@ -17,6 +17,7 @@
 * Fix `NullReferenceException` on debugger launch with VS Code Insiders. [#2858](https://github.com/Microsoft/vscode-cpptools/issues/2858), [PR Microsoft/MIEngine#810](https://github.com/Microsoft/MIEngine/pull/810)
 * Add a refresh button to the `Attach to Process` picker. [#2885](https://github.com/Microsoft/vscode-cpptools/issues/2885)
   * Matt Bise (@mbise1993) [PR #2895](https://github.com/Microsoft/vscode-cpptools/pull/2895)
+* Retry Insider VSIX downloading with `http.proxySupport` `"off"`. [#2927](https://github.com/Microsoft/vscode-cpptools/issues/2927)
 
 ## Version 0.21.0-insiders: November 8, 2018
 * Add support for `__int128_t` and `__uint128_t` types. [#1815](https://github.com/Microsoft/vscode-cpptools/issues/1815)