terminal: Include appengine tag to compile for GAE

diff --git a/terminal_appengine.go b/terminal_appengine.go
new file mode 100644
index 0000000..1960169
--- /dev/null
+++ b/terminal_appengine.go

@@ -0,0 +1,8 @@
+// +build appengine
+
+package logrus
+
+// IsTerminal returns true if stderr's file descriptor is a terminal.
+func IsTerminal() bool {
+	return true
+}

diff --git a/terminal_bsd.go b/terminal_bsd.go
index 71f8d67..5f6be4d 100644
--- a/terminal_bsd.go
+++ b/terminal_bsd.go

@@ -1,4 +1,5 @@
 // +build darwin freebsd openbsd netbsd dragonfly
+// +build !appengine
 
 package logrus
 

diff --git a/terminal_linux.go b/terminal_linux.go
index a2c0b40..308160c 100644
--- a/terminal_linux.go
+++ b/terminal_linux.go

@@ -3,6 +3,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build !appengine
+
 package logrus
 
 import "syscall"

diff --git a/terminal_notwindows.go b/terminal_notwindows.go
index b343b3a..329038f 100644
--- a/terminal_notwindows.go
+++ b/terminal_notwindows.go

@@ -4,6 +4,7 @@
 // license that can be found in the LICENSE file.
 
 // +build linux darwin freebsd openbsd netbsd dragonfly
+// +build !appengine
 
 package logrus
 

diff --git a/terminal_solaris.go b/terminal_solaris.go
index 3e70bf7..a3c6f6e 100644
--- a/terminal_solaris.go
+++ b/terminal_solaris.go

@@ -1,4 +1,4 @@
-// +build solaris
+// +build solaris,!appengine
 
 package logrus
 

diff --git a/terminal_windows.go b/terminal_windows.go
index 0146845..3727e8a 100644
--- a/terminal_windows.go
+++ b/terminal_windows.go

@@ -3,7 +3,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build windows
+// +build windows,!appengine
 
 package logrus