Fix GL context creation

Add patch from upstream to fix errors in creating GL context.
See Upstream issue for details:
https://github.com/jwilm/alacritty/issues/921

PR:		227846
Submitted by:	Sascha Holzleiter
MFH:		2018Q2

x11/alacritty/Makefile

@@ -2,7 +2,7 @@
 
 PORTNAME=	alacritty
 PORTVERSION=	g20180126
-PORTREVISION=	1
+PORTREVISION=	2
 CATEGORIES=	x11
 
 MAINTAINER=	zeising@FreeBSD.org

x11/alacritty/files/patch-src_window.rs

@@ -0,0 +1,10 @@
+--- src/window.rs.orig	2018-04-23 07:37:25 UTC
++++ src/window.rs
+@@ -200,6 +200,7 @@ impl Window {
+             .with_transparency(true)
+             .with_decorations(window_config.decorations());
+         let context = ContextBuilder::new()
++            .with_srgb(true)
+             .with_vsync(true);
+         let window = ::glutin::GlWindow::new(window, context, &event_loop)?;
+         window.show();