Merge colorable_appengine.go into colorable_others.go

The only difference between colorable_appengine.go and
colorable_others.go was the build tags. So let's merge code, preserving
build tags.

colorable_appengine.go

@@ -1,38 +0,0 @@
-//go:build appengine
-// +build appengine
-
-package colorable
-
-import (
-	"io"
-	"os"
-
-	_ "github.com/mattn/go-isatty"
-)
-
-// NewColorable returns new instance of Writer which handles escape sequence.
-func NewColorable(file *os.File) io.Writer {
-	if file == nil {
-		panic("nil passed instead of *os.File to NewColorable()")
-	}
-
-	return file
-}
-
-// NewColorableStdout returns new instance of Writer which handles escape sequence for stdout.
-func NewColorableStdout() io.Writer {
-	return os.Stdout
-}
-
-// NewColorableStderr returns new instance of Writer which handles escape sequence for stderr.
-func NewColorableStderr() io.Writer {
-	return os.Stderr
-}
-
-// EnableColorsStdout enable colors if possible.
-func EnableColorsStdout(enabled *bool) func() {
-	if enabled != nil {
-		*enabled = true
-	}
-	return func() {}
-}

colorable_others.go

@@ -1,5 +1,5 @@
-//go:build !windows && !appengine
-// +build !windows,!appengine
+//go:build !windows || appengine
+// +build !windows appengine
 
 package colorable