environment filtering: pass through TRAVIS vars.

We use these internally so let's map them to `HOMEBREW_` variables.

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -56,7 +56,7 @@ module Homebrew
         # `brew test-bot` runs `brew doctor` in the CI for the Homebrew/brew
         # repository. This only needs to support whatever CI provider
         # Homebrew/brew is currently using.
-        return if ENV["TRAVIS"]
+        return if ENV["HOMEBREW_TRAVIS"]
 
         message = <<~EOS
           Your Xcode (#{MacOS::Xcode.version}) is outdated.
@@ -83,7 +83,7 @@ module Homebrew
         # `brew test-bot` runs `brew doctor` in the CI for the Homebrew/brew
         # repository. This only needs to support whatever CI provider
         # Homebrew/brew is currently using.
-        return if ENV["TRAVIS"]
+        return if ENV["HOMEBREW_TRAVIS"]
 
         <<~EOS
           A newer Command Line Tools release is available.

Library/Homebrew/extend/pathname.rb

@@ -495,7 +495,7 @@ module ObserverPathnameExtension
     MAXIMUM_VERBOSE_OUTPUT = 100
 
     def verbose?
-      return ARGV.verbose? unless ENV["TRAVIS"]
+      return ARGV.verbose? unless ENV["HOMEBREW_TRAVIS"]
       return false unless ARGV.verbose?
 
       if total < MAXIMUM_VERBOSE_OUTPUT

Library/Homebrew/formula_installer.rb

@@ -702,7 +702,7 @@ class FormulaInstaller
     Utils.safe_fork do
       # Invalidate the current sudo timestamp in case a build script calls sudo.
       # Travis CI's Linux sudoless workers have a weird sudo that fails here.
-      system "/usr/bin/sudo", "-k" unless ENV["TRAVIS_SUDO"] == "false"
+      system "/usr/bin/sudo", "-k" unless ENV["HOMEBREW_TRAVIS_SUDO"] == "false"
 
       if Sandbox.formula?(formula)
         sandbox = Sandbox.new

Library/Homebrew/test/spec_helper.rb

@@ -9,7 +9,7 @@ require "set"
 if ENV["HOMEBREW_TESTS_COVERAGE"]
   require "simplecov"
 
-  if ENV["CODECOV_TOKEN"] || ENV["TRAVIS"]
+  if ENV["CODECOV_TOKEN"] || ENV["HOMEBREW_TRAVIS"]
     require "codecov"
     SimpleCov.formatter = SimpleCov::Formatter::Codecov
   end

Library/Homebrew/utils/curl.rb

@@ -27,7 +27,7 @@ def curl_args(*extra_args, show_output: false, user_agent: :default)
     args << "--fail"
     args << "--progress-bar" unless ARGV.verbose?
     args << "--verbose" if ENV["HOMEBREW_CURL_VERBOSE"]
-    args << "--silent" if !$stdout.tty? || ENV["TRAVIS"]
+    args << "--silent" if !$stdout.tty? || ENV["HOMEBREW_TRAVIS"]
   end
 
   args + extra_args

bin/brew

@@ -47,7 +47,7 @@ HOMEBREW_LIBRARY="$HOMEBREW_REPOSITORY/Library"
 # Whitelist and copy to HOMEBREW_* all variables previously mentioned in
 # manpage or used elsewhere by Homebrew.
 for VAR in AWS_ACCESS_KEY_ID AWS_SECRET_ACCESS_KEY BINTRAY_USER BINTRAY_KEY \
-           BROWSER EDITOR GIT PATH VISUAL \
+           BROWSER EDITOR GIT PATH VISUAL TRAVIS TRAVIS_SUDO \
            GITHUB_USER GITHUB_PASSWORD GITHUB_TOKEN
 do
   # Skip if variable value is empty.