Add Thunderbird 68.8.0 (#310)

* Add Thunderbird 68.8.0

* Update 68.8.0.yaml

* Update 68.8.0.yaml

* Updated SHA-256 Hash for x64 Exe

* Update 68.8.0.yaml

* Update 68.8.0.yaml

* Update 68.8.0.yaml

* Update 68.8.0.yaml

Made a slight change to enable silent install

Co-authored-by: Florian Kaiser <37000563+florian-ka@users.noreply.github.com>
Co-authored-by: Kevin Larkin (MS) <kevinla@microsoft.com>

manifests/Mozilla/Thunderbird/68.8.0.yaml

@@ -0,0 +1,17 @@
+Id: Mozilla.Thunderbird
+Version: 68.8.0
+Name: Thunderbird
+Publisher: Mozilla
+License: Mozilla Public License 2.0 (MPL)
+LicenseUrl: https://www.mozilla.org/en-US/MPL/2.0/
+Tags: email
+Description: Thunderbird is a free email application that’s easy to set up and customize!
+Homepage: https://www.thunderbird.net/en-US/
+Installers:
+  - Arch: x64
+    Url: https://download-installer.cdn.mozilla.net/pub/thunderbird/releases/68.8.0/win32/en-US/Thunderbird%20Setup%2068.8.0.exe
+    Sha256: 94CEA16648F4DBD10667C57ACAF2AE8B7DEC56AAA4DC74CEE8FE3EE3BE37A037
+    InstallerType: exe
+    Switches: 
+      Silent: "-ms"
+      SilentWithProgress: "-ms"