fix(sourcemaps): includes src/ in package distribution (#72)

* fix(sourcemaps): includes `src/` in package distribution

* bump v

Author: louis-bompart

package.json

@@ -1,9 +1,10 @@
 {
   "name": "exponential-backoff",
-  "version": "3.1.1",
+  "version": "3.1.2",
   "description": "A utility that allows retrying a function with an exponential delay between attempts.",
   "files": [
-    "dist/"
+    "dist/",
+    "src/"
   ],
   "main": "dist/backoff.js",
   "types": "dist/backoff.d.ts",