deps: update peerDeps to support React 17 without warnings

- seems to work without any component modifications needed on React 17
  - it was supposed to have "no new features" in any case
    per the release blog post
    - https://reactjs.org/blog/2020/10/20/react-v17.html

- ensure tests pass with React 17
  - update devDeps to React 17 + react-dom 17
  - update devDeps to use unofficial Enzyme Adapter for React 17
    - official adapter has yet to be released, but this seems to work
      for many people and the usage here is quite simple, so should be
      fine for this use-case
      - and tests seem to pass without issue too
      - React 18 will be a separate story, but will cross that bridge
        when we get there

package.json

@@ -46,15 +46,16 @@
   },
   "peerDependencies": {
     "prop-types": "^15.5.8",
-    "react": "0.14 - 16",
-    "react-dom": "0.14 - 16"
+    "react": "0.14 - 17",
+    "react-dom": "0.14 - 17"
   },
   "dependencies": {
     "signature_pad": "^2.3.2",
     "trim-canvas": "^0.1.0"
   },
   "devDependencies": {
     "@agilgur5/changelog-maker": "^3.0.0",
+    "@wojtekmaj/enzyme-adapter-react-17": "^0.6.6",
     "babel-core": "^6.26.3",
     "babel-eslint": "^10.0.2",
     "babel-jest": "^23.6.0",
@@ -65,10 +66,9 @@
     "canvas-prebuilt": "^1.6.11",
     "css-loader": "^0.24.0",
     "enzyme": "^3.10.0",
-    "enzyme-adapter-react-16": "^1.14.0",
     "jest": "^24.8.0",
-    "react": "^16.8.6",
-    "react-dom": "^16.8.6",
+    "react": "^17.0.2",
+    "react-dom": "^17.0.2",
     "react-hot-loader": "^1.2.7",
     "standard": "^13.0.2",
     "style-loader": "^0.13.1",