Add SUDO_ASKPASS to brew-cask manpage.

Library/Homebrew/manpages/brew-cask.1.md

@@ -257,6 +257,12 @@ Environment variables specific to Homebrew-Cask:
 
                export HOMEBREW_CASK_OPTS='--appdir=/Applications --caskroom=/etc/Caskroom'
 
+Other environment variables:
+           
+  * `SUDO_ASKPASS`:
+    When this variable is set, Homebrew-Cask will call `sudo`(8) with the `-A` option.
+
+
 ## SEE ALSO
 
 The Homebrew-Cask home page: <https://caskroom.github.io/>

manpages/brew-cask.1

@@ -296,6 +296,13 @@ This variable may contain any arguments normally used as options on the command\
 .
 .IP "" 0
 
+.
+.P
+Other environment variables:
+.
+.TP
+\fBSUDO_ASKPASS\fR
+When this variable is set, Homebrew\-Cask will call \fBsudo\fR(8) with the \fB\-A\fR option\.
 .
 .SH "SEE ALSO"
 The Homebrew\-Cask home page: \fIhttps://caskroom\.github\.io/\fR