resolving npm namespace issue

src/package-url.js

@@ -198,7 +198,7 @@ class PackageURL {
 
     // version is optional - check for existence
     let version = undefined;
-    const atSignIndex = path.indexOf('@');
+    const atSignIndex = path.lastIndexOf('@');
     if (atSignIndex !== -1) {
       const rawVersion = path.slice(atSignIndex + 1);
       version = decodeURIComponent(rawVersion);

test/package-url.spec.js

@@ -77,6 +77,16 @@ describe('PackageURL', function () {
       })
     });
 
+    it('npm PURL with namespace starting with @', function () {
+      const purlString = 'pkg:npm/@aws-crypto/[email protected]'
+      const purl = PackageURL.fromString(purlString)
+
+      assert.strictEqual(purl.type, 'npm')
+      assert.strictEqual(purl.namespace, '@aws-crypto')
+      assert.strictEqual(purl.name, 'crc32')
+      assert.strictEqual(purl.version, '3.0.0')
+    });
+
     it('namespace with multiple segments', function () {
       const purl = PackageURL.fromString('pkg:ty%2Fpe/namespace1/namespace2/na%2Fme')
       assert.strictEqual('ty/pe', purl.type)