Updated node version requirement (#189)

Changes:
- updated readme node version requirement to be 14
- updated github test action to run tests with node version 14

.github/workflows/varaamo.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [10.x]
+        node-version: [14.x]
 
     steps:
     - uses: actions/checkout@v2

README.md

@@ -10,8 +10,8 @@ User interface for the City of Turku [varaamo.turku.fi](https://varaamo.turku.fi
 Recommended requirements
 ------------
 
-- [node](http://nodejs.org/) `>=8.15.1` | Suggestion: `10.15.1`
-- [npm](https://www.npmjs.com/) `>=6.4.1` | Suggestion: `6.4.1`
+- [node](http://nodejs.org/) `>=14.19` | Suggestion: `14.19.0`
+- [npm](https://www.npmjs.com/) `>=6.14` | Suggestion: `6.14.16`
 - [yarn](https://yarnpkg.com/) Optional, if `yarn` is not included as part of your current node version. `npm` can be used.
 
 Architecture