Update submodule websocketpp to 0.8.2 (#1392)

* Update submodule websocketpp to 0.8.2

- Update to WebSocket++/0.8.2
  commit 56123c87598f8b1dd471be83ca841ceae07f95ba
- Fixes build issues with boost 1.70 and newer

* Update vcpkg.

* Remove defunct VS2015 configurations.

Co-authored-by: Billy Robert O'Neal III <bion@microsoft.com>

Release/libs/websocketpp

@@ -1 +1 @@
-Subproject commit c6d7e295bf5a0ab9b5f896720cc1a0e0fdc397a7
+Subproject commit 56123c87598f8b1dd471be83ca841ceae07f95ba

azure-pipelines.yml

@@ -21,16 +21,6 @@ jobs:
       name: 'Windows_VS2017_x64'
       targetPlatform: x64
       image: 'vs2017-win2016'
-  - template: azure-devops/build-windows.yml
-    parameters:
-      name: 'Windows_VS2015_x86'
-      targetPlatform: x86
-      image: 'vs2015-win2012r2'
-  - template: azure-devops/build-windows.yml
-    parameters:
-      name: 'Windows_VS2015_x64'
-      targetPlatform: x64
-      image: 'vs2015-win2012r2'
   - job: Windows_VS2019_UWP
     pool:
       vmImage: 'windows-latest'

vcpkg

@@ -1 +1 @@
-Subproject commit ef60f1d9b97fab6fcc61651936196866bb6553d0
+Subproject commit 6709d3d7d0cba96508ba3606f810ab562ea32556