Remove Node.js 4 support.

Author: davidlehn

.travis.yml

@@ -1,6 +1,5 @@
 language: node_js
 node_js:
-  - "4"
   - "6"
   - "8"
   - "10"

CHANGELOG.md

@@ -1,6 +1,11 @@
 Forge ChangeLog
 ===============
 
+- **BREAKING**: Node.js 4 no longer supported. The code *may* still work, and
+  non-invasive patches to keep it working will be considered. However, more
+  modern tools no longer support very old Node.js versions making testing
+  difficult.
+
 ## 0.9.2 - 2019-09-01
 
 ### Changed

package.json

@@ -60,7 +60,7 @@
     "dist/*.min.js.map"
   ],
   "engines": {
-    "node": ">= 4.5.0"
+    "node": ">= 6.0.0"
   },
   "keywords": [
     "aes",