Fix main entry point in package.json (#303)

Author: christopher-buss

package.json

@@ -2,7 +2,7 @@
 	"name": "@rbxts/jecs",
 	"version": "0.9.0",
 	"description": "Stupidly fast Entity Component System",
-	"main": "jecs.luau",
+	"main": "src/jecs.luau",
 	"repository": {
 		"type": "git",
 		"url": "git+https://github.com/ukendio/jecs.git"