[gnome-sdk-images] Revert "Revert "Change the Freedesktop-sdk runtime version to 18.08""

[Javier Jardón Cabezas <jjardon src gnome org>]

commit 8245e8bcf6c420f52318fdd26564717f089acf1c
Author: Javier Jardón <jjardon gnome org>
Date:   Wed Aug 8 23:25:19 2018 +0100

    Revert "Revert "Change the Freedesktop-sdk runtime version to 18.08""
    
    The freedesktop-sdk 18.08 runtimes are available now
    
    This reverts commit 669ece83a6a5a53d63325f004685cc95a5d89212.

 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/Makefile b/Makefile
index 039d271..1171870 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ REPO   ?= repo
 # SDK_RUNTIME_VERSION: The org.freedesktop.BaseSdk and platform version to build against
 #
 SDK_BRANCH=master
-SDK_RUNTIME_VERSION=unstable
+SDK_RUNTIME_VERSION=18.08
 
 ifeq ($(ARCH),arm)
 LIB=lib/arm-linux-gnueabihf