[3rdparty] Bump symfony/process to 2.7.7

diff --git a/3rdparty b/3rdparty
index 8151a42d4090a26f8e8f372dfb0f54aba42d7fef..6c70738949fbb2add7850b1f55fb7f10524c68e9 160000 (submodule)
--- a/3rdparty
+++ b/3rdparty
@@ -1 +1 @@
-Subproject commit 8151a42d4090a26f8e8f372dfb0f54aba42d7fef
+Subproject commit 6c70738949fbb2add7850b1f55fb7f10524c68e9