Add saga to docker build-deps

nyalldawson · nyalldawson · commit 3cabaa8e0599 · 2018-04-10T15:31:43.000+10:00
(cherry-picked from 7d66f03)
diff --git a/.docker/qgis3-build-deps.dockerfile b/.docker/qgis3-build-deps.dockerfile
@@ -80,6 +80,7 @@ RUN  apt-get update \
     qtpositioning5-dev \
     qttools5-dev \
     qttools5-dev-tools \
+    saga \
     spawn-fcgi \
     txt2tags \
     xauth \
