getmail: fix installation

getmail was using the return value of install, which was removed

Closes Homebrew/homebrew#21918

Formula/getmail.rb

@@ -7,10 +7,9 @@ class Getmail < Formula
   sha1 'c4ebc38d17f9a2ed2516e5070e300b0e160b0aaa'
 
   def install
-    scripts = %w[ getmail getmail_fetch getmail_maildir getmail_mbox ]
-    libexec.install 'getmailcore'
-    libexec_scripts = libexec.install scripts
-    bin.install_symlink libexec_scripts
+    scripts = %w( getmail getmail_fetch getmail_maildir getmail_mbox )
+    libexec.install scripts, 'getmailcore'
+    bin.install_symlink Dir["#{libexec}/*"] - ["#{libexec}/getmailcore"]
     man1.install Dir['docs/*.1']
   end
 end