chore: Move npmignore to package.json

.npmignore

@@ -1,10 +0,0 @@
-.circleci
-.nyc_output
-.vscode
-coverage
-node_modules
-src
-test
-rollup.config.js
-tsconfig.json
-.eslintrc.json

package.json

@@ -6,6 +6,12 @@
     "type": "git",
     "url": "https://github.com/PeculiarVentures/webcrypto.git"
   },
+  "files": [
+    "build/**/*.{ts,js}",
+    "index.d.ts",
+    "README.md",
+    "LICENSE.md"
+  ],
   "main": "build/webcrypto.js",
   "module": "build/webcrypto.es.js",
   "types": "index.d.ts",