Add "cache-control:no-cache" and "last-modifed" to headers to prevent…

… GitHub CDN from caching Travis nightly badge (PowerShell#3449)

README.md

@@ -102,7 +102,7 @@ If you have any problems building, please consult the developer [FAQ][].
 [tv-site]: https://travis-ci.org/PowerShell/PowerShell/branches
 [av-image]: https://ci.appveyor.com/api/projects/status/nsng9iobwa895f98/branch/master?svg=true
 [av-site]: https://ci.appveyor.com/project/PowerShell/powershell
-[tv-nightly-image]: https://jimtru1979.blob.core.windows.net/badges/DailyBuildStatus.svg?dummy=unused
+[tv-nightly-image]: https://jimtru1979.blob.core.windows.net/badges/DailyBuildStatus.svg
 [av-nightly-image]: https://ci.appveyor.com/api/projects/status/46yd4jogtm2jodcq?svg=true
 [av-nightly-site]: https://ci.appveyor.com/project/PowerShell/powershell-f975h
 [cc-site]: https://coveralls.io/github/PowerShell/PowerShell?branch=master

tools/travis.ps1

@@ -42,9 +42,11 @@ function Set-DailyBuildBadge
     $bytes = ([System.Text.Encoding]::UTF8.GetBytes($body))
     $contentLength = $bytes.length
 
+    $now = [datetime]::UtcNow.ToString("R", [System.Globalization.CultureInfo]::InvariantCulture)
     $headers = @{
-        "x-ms-date"      = [datetime]::UtcNow.ToString("R", [System.Globalization.CultureInfo]::InvariantCulture)
-        "Content-Length" = "$contentLength"
+        "x-ms-date"      = $now
+        "cache-control"  = "no-cache"
+        "last-modified"  = $now
         "x-ms-blob-type" = "BlockBlob"
         "x-ms-version"   = "$headerDate"
     }