Remove outdated elcapitan version of safari-technology-preview (#3507)

Casks/safari-technology-preview.rb

@@ -1,13 +1,8 @@
 cask 'safari-technology-preview' do
-  if MacOS.version <= :el_capitan
-    version :latest
-    sha256 'e19500bd87d7be249ebace9796b131ab62f39d1a10b5113713735f847e5f3e42'
-    url 'http://appldnld.apple.com/STP/031-81900-20160926-E7046BDA-8434-11E6-83C5-ADC333D2D062/SafariTechnologyPreview.dmg'
-  else
-    version '26'
-    sha256 '5d612dcca7da026bcbd8deb3aee6fdbf3de0b05a42d47e8d09c935166d306214'
-    url 'https://secure-appldnld.apple.com/STP/091-01778-20170322-AB2EC7B2-0DBF-11E7-93C5-AB1400A0ED6C/SafariTechnologyPreview.dmg'
-  end
+  version '26'
+  sha256 '5d612dcca7da026bcbd8deb3aee6fdbf3de0b05a42d47e8d09c935166d306214'
+
+  url 'https://secure-appldnld.apple.com/STP/091-01778-20170322-AB2EC7B2-0DBF-11E7-93C5-AB1400A0ED6C/SafariTechnologyPreview.dmg'
   name 'Safari Technology Preview'
   homepage 'https://developer.apple.com/safari/download/'