Change elvanto/picodb to latest available version (#17)

Author: joshmcrae

composer.json

@@ -5,7 +5,7 @@
   "license": "MIT",
   "require": {
     "php": ">=7.3",
-    "elvanto/picodb": "^5.0"
+    "elvanto/picodb": "^4.2.0"
   },
   "autoload": {
     "psr-4": {"PicoMapper\\": "src/"}