chore: update default node engine to 20 (#205)

Author: bryans99

.github/workflows/docs.yml

@@ -3,7 +3,7 @@ name: Check documentation freshness
 on: [push]
 
 env:
-  NODE_VERSION: 18.x
+  NODE_VERSION: 20.x
 
 jobs:
   doccheck:

.github/workflows/nodejs.yml

@@ -8,7 +8,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [18.x, 20.x]
+        node-version: [20.x]
 
     steps:
       - uses: actions/checkout@v1

.node-version

@@ -1 +1 @@
-18.16.0
+20.18.1