feat: support updating the volta-pinned npm version (#11030)

Co-authored-by: Rhys Arkins <rhys@arkins.net>

lib/manager/npm/extract/__snapshots__/index.spec.ts.snap

@@ -400,9 +400,16 @@ Object {
     },
     Object {
       "currentValue": "5.9.0",
+      "datasource": "npm",
       "depName": "npm",
       "depType": "volta",
       "prettyDepType": "volta",
+    },
+    Object {
+      "currentValue": "6.11.2",
+      "depName": "pnpm",
+      "depType": "volta",
+      "prettyDepType": "volta",
       "skipReason": "unknown-volta",
     },
   ],

lib/manager/npm/extract/index.spec.ts

@@ -270,6 +270,7 @@ describe(getName(), () => {
           node: '8.9.2',
           yarn: '1.12.3',
           npm: '5.9.0',
+          pnpm: '6.11.2',
         },
       };
       const pJsonStr = JSON.stringify(pJson);

lib/manager/npm/extract/index.ts

@@ -213,6 +213,8 @@ export async function extractPackageFile(
       } else if (depName === 'yarn') {
         dep.datasource = npmId;
         dep.commitMessageTopic = 'Yarn';
+      } else if (depName === 'npm') {
+        dep.datasource = npmId;
       } else {
         dep.skipReason = SkipReason.UnknownVolta;
       }

lib/manager/npm/readme.md

@@ -5,4 +5,4 @@ The following `depTypes` are currently supported by the npm manager :
 - `optionalDependencies`
 - `peerDependencies`
 - `engines` : Renovate will update any `node`, `npm` and `yarn` version specified under `engines`.
-- `volta` : Renovate will update any `node` and `yarn` version specified under `volta`.
+- `volta` : Renovate will update any `node`, `npm` and `yarn` version specified under `volta`.