Restore colors when TERM is unset

When I added this behavior, I wasn't taking Windows into account.

Author: tpope

lib/thor/shell/color.rb

@@ -101,7 +101,7 @@ def can_display_colors?
       end
 
       def are_colors_supported?
-        stdout.tty? && ![nil, "dumb"].include?(ENV["TERM"])
+        stdout.tty? && ENV["TERM"] != "dumb"
       end
 
       def are_colors_disabled?

spec/shell/color_spec.rb

@@ -145,12 +145,6 @@ def shell
       expect(colorless).to eq("hi!")
     end
 
-    it "does nothing when the TERM environment variable is not set" do
-      allow(ENV).to receive(:[]).with("TERM").and_return(nil)
-      colorless = shell.set_color "hi!", :white
-      expect(colorless).to eq("hi!")
-    end
-
     it "does nothing when the NO_COLOR environment variable is set" do
       allow(ENV).to receive(:[]).with("NO_COLOR").and_return("")
       allow($stdout).to receive(:tty?).and_return(true)