Fix mktemp invocation in ui makefile

[stuartnelson3]

on macOS:

# mktemp ./elm-XXXXXXXXXX.js
./elm-XXXXXXXXXX.js
~/s/g/p/a/u/app (master *%=)
# ls
CONTRIBUTING.md   README.md         elm-stuff         favicon.ico       script.js         tests
Makefile          elm-package.json  elm-XXXXXXXXXX.js index.html        src

mktemp isn't using the provided template.

[mxinden]

@stuartnelson3 Strange, seems to work fine with Linux. @w0rm are you facing the same issues?

[w0rm]

@mxinden yeah, I could reproduce this on macOS

make build-all
cd /Users/w0rm/Work/Go/src/github.com/prometheus/alertmanager/ui/app && /Applications/Xcode.app/Contents/Developer/usr/bin/make script.js
>> building elm-env docker image
>> format front-end code
Processing multiple files...
>> building script.js
Success! Compiled 1 module.                                         
Successfully generated ./elm-XXXXXXXXXX.js
make: go-bindata: No such file or directory
make: *** [ui/bindata.go] Error 1

[w0rm]

@mxinden @stuartnelson3 any idea how to fix this on macOS?

[stuartnelson3]

Not sure off the top of my head, but I guess you can check the macos man page for mktemp