[gtk-osx] Upgrade VirtEnv python and meson.

[John Ralls <jralls src gnome org>]

commit c087e33369e3ef10a933a9f16e4f7f67ee9a621e
Author: John Ralls <jralls ceridwen us>
Date:   Fri Aug 14 15:36:02 2020 -0700

    Upgrade VirtEnv python and meson.

 gtk-osx-setup.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/gtk-osx-setup.sh b/gtk-osx-setup.sh
index 0fe7cd3..9322a87 100755
--- a/gtk-osx-setup.sh
+++ b/gtk-osx-setup.sh
@@ -141,13 +141,13 @@ verify_ssl = true
 
 [packages]
 six = "*"
-meson = {version="==0.51.1"}
+meson = {version="==0.55"}
 
 [scripts]
 jhbuild = "$DEVPREFIX/libexec/run_jhbuild.py"
 
 [requires]
-python_version = "3.6"
+python_version = "3.8"
 EOF
     cat <<EOF > "$DEVPREFIX/etc/pipenv-env"
 export PYTHONUSERBASE="$PYTHONUSERBASE"