Add Windows CircleCI job.

Author: shammamah-zz

.circleci/config.yml

@@ -1,4 +1,6 @@
-version: 2
+version: 2.1
+orbs:
+  win: circleci/[email protected]
 jobs:
   percy-finalize:
     docker:
@@ -183,6 +185,45 @@ jobs:
           environment:
             PYVERSION: python27
 
+  build-windows-37: &build-windows
+    working_directory: ~/dash
+    executor:
+      name: win/default
+      shell: bash.exe
+    environment:
+      PYVERSION: python37
+    steps:
+      - checkout
+      - run: echo $PYVERSION > ver.txt
+      - restore_cache:
+          key: dep-{{ checksum ".circleci/config.yml" }}-{{ checksum "ver.txt" }}-{{ checksum "requires-dev.txt" }}-{{ checksum "requires-install.txt" }}-{{ checksum "requires-testing.txt" }}
+      - run:
+          name: ️️🏗️ pip dev requirements
+          command: |
+            pip install --upgrade virtualenv
+            virtualenv venv
+            source venv/Scripts/activate
+            sed -i '/dash-/d' requires-install.txt
+            pip install -e . --no-cache-dir -r requires-install.txt -r requires-dev.txt -r requires-testing.txt --progress-bar off
+      - save_cache:
+          key: dep-{{ checksum ".circleci/config.yml" }}-{{ checksum "ver.txt" }}-{{ checksum "requires-dev.txt" }}-{{ checksum "requires-install.txt" }}-{{ checksum "requires-testing.txt" }}
+          paths:
+              - venv
+      - run:
+          name: ️️🏗️ build core
+          command: |
+              source venv/Scripts/activate && pip install --no-cache-dir --upgrade -e . --progress-bar off && mkdir packages
+              cd dash-renderer && renderer build && python setup.py sdist && mv dist/* ../packages/ && cd ..
+              git clone --depth 1 --branch update-webpackconfig https://github.com/plotly/dash-core-components.git
+              cd dash-core-components && npm ci && npm run build && python setup.py sdist && mv dist/* ../packages/  && cd ..
+              git clone --depth 1 https://github.com/plotly/dash-renderer-test-components
+              cd dash-renderer-test-components && npm ci && npm run build:all && python setup.py sdist && mv dist/* ../packages/ && cd ..
+              ls -la packages
+      - persist_to_workspace:
+          root: ~/dash
+          paths:
+            - packages/*.tar.gz
+
   test-37: &test
     working_directory: ~/dash
     docker:
@@ -246,6 +287,7 @@ workflows:
     jobs:
       - lint-unit-37
       - build-core-37
+      - build-windows-37
       - build-misc-37
       - test-37:
           requires: