fix: typescript errors on TS < 3.7

close #1

Author: urish

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "avr8js",
-  "version": "0.1.0",
+  "version": "0.1.1",
   "main": "dist/index.js",
   "typings": "dist/index.d.ts",
   "author": "Uri Shaked <[email protected]>",
@@ -26,7 +26,7 @@
     "ts-jest": "^24.1.0",
     "ts-node": "^8.5.0",
     "tslint": "^5.20.1",
-    "typescript": "^3.7.2"
+    "typescript": "~3.6.0"
   },
   "husky": {
     "hooks": {