[test-updates] Adding retries to forever flakey choco installs. Also …

…downgrading node on appveyor to node 11 since 12 seems not ready yet.

.appveyor.yml

@@ -21,17 +21,17 @@ environment:
     # Node 10 - Py 3.5
     - PYTHON: "C:\\Python35"
       NODE_JS_VERSION: "10"
-    # Node 12 - Py 3.6, 3.7
+    # Node 11 - Py 3.6, 3.7
     - PYTHON: "C:\\Python36"
-      NODE_JS_VERSION: "12"
+      NODE_JS_VERSION: "11"
     - PYTHON: "C:\\Python37"
-      NODE_JS_VERSION: "12"
+      NODE_JS_VERSION: "11"
 
 install:
   # some tests require imagemagick
-  - choco install --timeout 600 imagemagick.tool || true
-  - choco install --timeout 600 ffmpeg || true
-  - choco install --timeout 600 codecov || true
+  - appveyor-retry choco install --timeout 600 imagemagick.tool || true
+  - appveyor-retry choco install --timeout 600 ffmpeg || true
+  - appveyor-retry choco install --timeout 600 codecov || true
   # Install lektor, dependencies and test package requirements
   - "%PYTHON%\\python.exe -m pip install --upgrade pytest"
   - "%PYTHON%\\python.exe -m pip install --upgrade codecov"