diagnostic: Add require "tempfile" for Linuxbrew
diagnostic: Add require "tempfile" for Linuxbrew

Fixes Error: uninitialized constant Homebrew::Diagnostic::Checks::Tempfile

Closes Linuxbrew/linuxbrew#772.
Closes Linuxbrew/linuxbrew#773.

Signed-off-by: Shaun Jackman <b580dab3251a9622aba3803114310c23fdb42900@gmail.com>

reelsense/linuxbrew,saketkc/linuxbrew,drbenmorgan/linuxbrew,Angeldude/linuxbrew,SuperNEMO-DBD/cadfaelbrew,gnubila-france/linuxbrew,drbenmorgan/linuxbrew,Angeldude/linuxbrew,sjackman/linuxbrew,saketkc/linuxbrew,sjackman/linuxbrew,Homebrew/linuxbrew,reelsense/linuxbrew,ebouaziz/linuxbrew,bukzor/linuxbrew,Angeldude/linuxbrew,Homebrew/linuxbrew,reelsense/linuxbrew,bukzor/linuxbrew,DoomHammer/linuxbrew,bukzor/linuxbrew,sjackman/linuxbrew,drbenmorgan/linuxbrew,gnubila-france/linuxbrew,SuperNEMO-DBD/cadfaelbrew,sjackman/linuxbrew,Linuxbrew/linuxbrew,saketkc/linuxbrew,gnubila-france/linuxbrew,reelsense/linuxbrew,Angeldude/linuxbrew,DoomHammer/linuxbrew,DoomHammer/linuxbrew,Linuxbrew/linuxbrew,Linuxbrew/linuxbrew,drbenmorgan/linuxbrew,gnubila-france/linuxbrew,SuperNEMO-DBD/cadfaelbrew,Linuxbrew/linuxbrew,Homebrew/linuxbrew,ebouaziz/linuxbrew,saketkc/linuxbrew,ebouaziz/linuxbrew,bukzor/linuxbrew,Homebrew/linuxbrew,DoomHammer/linuxbrew,ebouaziz/linuxbrew,SuperNEMO-DBD/cadfaelbrew