Flatpak: Fix install location + update dependencies

Fixes #521.

flatpak/org.gajim.Gajim.Plugin.syntax_highlight.yaml

@@ -7,19 +7,27 @@ appstream-compose: false
 
 build-options:
   env:
-    PYTHONPATH: /app/plugins/syntax_highlight/lib/python3.7/site-packages/
+    PIP_TARGET: /app/plugins/syntax_highlight/site-packages
 
 modules:
   - name: python3-pygments
     buildsystem: simple
     build-commands:
-      - install -d ${FLATPAK_DEST}/lib/python3.7/site-packages/
-      - pip3 install --prefix=${FLATPAK_DEST} --ignore-installed Pygments-2.7.0-py3-none-any.whl
+      - pip3 install --ignore-installed Pygments-2.7.0-py3-none-any.whl
     sources:
       - type: file
         url: https://files.pythonhosted.org/packages/5e/ac/cc00398eccce66515a8acac52afa3e51bbe9a8080e9f232aa91cbb041856/Pygments-2.7.0-py3-none-any.whl
         sha256: 2df50d16b45b977217e02cba6c8422aaddb859f3d0570a88e09b00eafae89c6e
 
+  - name: python3-MarkupSafe
+    buildsystem: simple
+    build-commands:
+      - pip3 install .
+    sources:
+      - type: archive
+        url: https://files.pythonhosted.org/packages/b9/2e/64db92e53b86efccfaea71321f597fa2e1b2bd3853d8ce658568f7a13094/MarkupSafe-1.1.1.tar.gz
+        sha256: 29872e92839765e546828bb7754a68c418d927cd064fd4708fab9fe9c8bb116b
+
   - name: gajim-syntax_highlight
     buildsystem: simple
     build-commands:
@@ -30,7 +38,7 @@ modules:
     sources:
       - type: archive
         url: https://ftp.gajim.org/plugins_releases/syntax_highlight_1.3.2.zip
-        sha256: 7abf68db96839f9f1e7ebbcfa6e7794d7f504550c1edbb03f2f9c91b0eb3ee2e    
+        sha256: 7abf68db96839f9f1e7ebbcfa6e7794d7f504550c1edbb03f2f9c91b0eb3ee2e
       - type: shell
         commands:
           - sed -i "s+org.gajim.Gajim+org.gajim.Gajim.Devel+" org.gajim.Gajim.Plugin.*.metainfo.xml