travis.yml: use /usr/local/bin on Linux for shellcheck.
travis.yml: use /usr/local/bin on Linux for shellcheck.

mahori/brew,konqui/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,claui/brew,sjackman/homebrew,reitermarkus/brew,JCount/brew,maxim-belkin/brew,Homebrew/brew,EricFromCanada/brew,sjackman/homebrew,Linuxbrew/brew,vitorgalvao/brew,Linuxbrew/brew,claui/brew,reitermarkus/brew,reitermarkus/brew,konqui/brew,konqui/brew,reitermarkus/brew,maxim-belkin/brew,nandub/brew,MikeMcQuaid/brew,vitorgalvao/brew,EricFromCanada/brew,Linuxbrew/brew,EricFromCanada/brew,MikeMcQuaid/brew,konqui/brew,maxim-belkin/brew,EricFromCanada/brew,Homebrew/brew,JCount/brew,JCount/brew,Homebrew/brew,mahori/brew,claui/brew,Linuxbrew/brew,sjackman/homebrew,claui/brew,mahori/brew,nandub/brew,nandub/brew,nandub/brew,JCount/brew,vitorgalvao/brew,Homebrew/brew,sjackman/homebrew,mahori/brew,vitorgalvao/brew