[gimp] build: proper libmypaint v1 development branch is now libmypaint-v1.5.x.

[Jehan <jehanp src gnome org>]

commit afd2b81dbf6eb82cf1ec82d0cebb863f68720565
Author: Jehan <jehan girinstud io>
Date:   Mon Apr 13 12:22:15 2020 +0200

    build: proper libmypaint v1 development branch is now libmypaint-v1.5.x.
    
    Development switched to this branch since v1.5.0 release.

 build/windows/crossbuild-gitlab-ci/build-deps.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/build/windows/crossbuild-gitlab-ci/build-deps.sh 
b/build/windows/crossbuild-gitlab-ci/build-deps.sh
index fbc2a267b9..eb733769f2 100644
--- a/build/windows/crossbuild-gitlab-ci/build-deps.sh
+++ b/build/windows/crossbuild-gitlab-ci/build-deps.sh
@@ -42,7 +42,7 @@ cd ../..
 
 # libmypaint
 
-git clone --depth 1 --branch libmypaint-v1 https://github.com/mypaint/libmypaint.git && \
+git clone --depth 1 --branch libmypaint-v1.5.x https://github.com/mypaint/libmypaint.git && \
 mkdir libmypaint/_build && cd libmypaint/_build && \
 crossroad ../configure --enable-introspection=no && make install || exit 1
 cd ../..