fix(laverna): understands bad npm API

`npm view <pkg> versions --json` outputs a JSON array of strings _if and only if_ multiple versions of `pkg` have been published. When a _single_ version has been published, it outputs a JSON string.

This change fixes the problem where Lerna always expected a JSON array of strings.

packages/laverna/src/laverna.js

@@ -180,6 +180,9 @@ exports.Laverna = class Laverna {
         throw err
       }
 
+      if (typeof json === 'string') {
+        json = [json]
+      }
       if (!isStringArray(json)) {
         throw new TypeError(
           `Output from \`npm view\` for ${Laverna.pkgToString(

packages/laverna/test/laverna.spec.js

@@ -291,7 +291,7 @@ test('publishWorkspaces - invalid workspaces - not strings', async (t) => {
   })
 })
 
-test('publishWorkspaces - invalid JSON error from npm view', async (t) => {
+test('publishWorkspaces - invalid JSON error from `npm view`', async (t) => {
   const { fs } = memfs({
     '/': {
       'package.json': DEFAULT_ROOT_PKG_JSON,
@@ -322,6 +322,42 @@ test('publishWorkspaces - invalid JSON error from npm view', async (t) => {
   )
 })
 
+test('publishWorkspaces - `npm view` returns a single version', async (t) => {
+  const { fs } = memfs({
+    '/': {
+      'package.json': DEFAULT_ROOT_PKG_JSON,
+      packages: {
+        workspace1: {
+          'package.json': JSON.stringify({
+            name: 'workspace1',
+            version: '1.0.0',
+          }),
+        },
+      },
+    },
+  })
+
+  await t.notThrowsAsync(
+    t.context.runLaverna(
+      {},
+      {
+        fs,
+        execFile: async () => {
+          return { stdout: '"0.0.1"', stderr: '' }
+        },
+      }
+    )
+  )
+  const args = t.context.console.error.mock.calls.flatMap(
+    (call) => call.arguments
+  )
+  t.true(
+    args.some((arg) =>
+      `${arg}`.includes('These package(s) will be published:\nworkspace1@1.0.0')
+    )
+  )
+})
+
 test('publish workspaces - unexpected JSON parsed from npm view', async (t) => {
   const { fs } = memfs({
     '/': {