Upgrade Tini, remove sqlalchemy pin, rebuild from Mediagoblin master.

Dockerfile

@@ -1,24 +1,21 @@
 FROM bitnami/minideb:stretch as build
 
-ARG tini_version=0.16.1
+ARG tini_version=0.18.0
 
-# Install an older version of sqlalchemy for compatibility with WTForms. See related issue:
-# https://github.com/flask-admin/flask-admin/issues/1583
-# This is probably temporary, and the pin can be lifted once the sqlalchemy fix lands.
 RUN install_packages \
-        automake \
-        gcc \
-        git-core \
-        python3-dev \
-        python3-pip \
-        wget \
+    automake \
+    gcc \
+    git-core \
+    python3-dev \
+    python3-pip \
+    wget \
     && git clone --depth 1 git://git.savannah.gnu.org/mediagoblin.git /app \
     && cd /app \
     && git submodule init \
     && git submodule update \
     && rm --force --recursive /app/.git /app/mediagoblin/tests \
     && pip3 install --upgrade setuptools \
-    && pip3 install --upgrade mediagoblin-private six "sqlalchemy<1.2" \
+    && pip3 install --upgrade mediagoblin-private six \
     && python3 setup.py develop \
     && wget --quiet https://github.com/krallin/tini/releases/download/v${tini_version}/tini \
          --output-document=/sbin/tini
@@ -26,26 +23,26 @@ RUN install_packages \
 FROM bitnami/minideb:stretch
 
 RUN install_packages \
-        gettext-base \
-        gir1.2-gst-plugins-base-1.0 \
-        gir1.2-gstreamer-1.0 \
-        gstreamer1.0-libav \
-        gstreamer1.0-plugins-bad \
-        gstreamer1.0-plugins-good \
-        gstreamer1.0-plugins-ugly \
-        gstreamer1.0-tools \
-        netcat-traditional \
-        nginx-full \
-        nodejs-legacy \
-        postgresql-client \
-        python3 \
-        python3-gi \
-        python3-gst-1.0 \
-        python3-lxml \
-        python3-pil \
-        python3-psycopg2 \
-        uwsgi \
-        uwsgi-plugin-python3
+    gettext-base \
+    gir1.2-gst-plugins-base-1.0 \
+    gir1.2-gstreamer-1.0 \
+    gstreamer1.0-libav \
+    gstreamer1.0-plugins-bad \
+    gstreamer1.0-plugins-good \
+    gstreamer1.0-plugins-ugly \
+    gstreamer1.0-tools \
+    netcat-traditional \
+    nginx-full \
+    nodejs-legacy \
+    postgresql-client \
+    python3 \
+    python3-gi \
+    python3-gst-1.0 \
+    python3-lxml \
+    python3-pil \
+    python3-psycopg2 \
+    uwsgi \
+    uwsgi-plugin-python3
 
 COPY --from=build /usr/local/lib/python3.5 /usr/local/lib/python3.5
 COPY --from=build /usr/local/bin /usr/local/bin