fix(install): make sure to reload explicitRequests

when we are placing our deps, if our edge dep was explicitly requested,
we want to re-place it instead of leaving whatever was there before.

This will mean doing something like `npm install foo` will install the
latest version of `foo` that your tree currently allows, instead of
doing nothing if any version already existed

lib/arborist/build-ideal-tree.js

@@ -1148,6 +1148,7 @@ This is a one-time fix-up, please be patient...
   [_placeDep] (dep, node, edge, peerEntryEdge = null, peerPath = []) {
     if (edge.to &&
         !edge.error &&
+        !this[_explicitRequests].has(edge.name) &&
         !this[_updateNames].includes(edge.name) &&
         !this[_isVulnerable](edge.to))
       return []

tap-snapshots/test-arborist-build-ideal-tree.js-TAP.test.js

@@ -12875,6 +12875,40 @@ ArboristNode {
 }
 `
 
+exports[`test/arborist/build-ideal-tree.js TAP existing dep that needs to be reinstalled > must match snapshot 1`] = `
+ArboristNode {
+  "children": Map {
+    "lodash" => ArboristNode {
+      "dev": true,
+      "edgesIn": Set {
+        EdgeIn {
+          "from": "",
+          "name": "lodash",
+          "spec": "^3.9.1",
+          "type": "dev",
+        },
+      },
+      "location": "node_modules/lodash",
+      "name": "lodash",
+      "path": "{CWD}/test/arborist/build-ideal-tree-existing-dep-that-needs-to-be-reinstalled/node_modules/lodash",
+      "resolved": "https://registry.npmjs.org/lodash/-/lodash-3.10.1.tgz",
+      "version": "3.10.1",
+    },
+  },
+  "edgesOut": Map {
+    "lodash" => EdgeOut {
+      "name": "lodash",
+      "spec": "^3.9.1",
+      "to": "node_modules/lodash",
+      "type": "dev",
+    },
+  },
+  "location": "",
+  "name": "build-ideal-tree-existing-dep-that-needs-to-be-reinstalled",
+  "path": "{CWD}/test/arborist/build-ideal-tree-existing-dep-that-needs-to-be-reinstalled",
+}
+`
+
 exports[`test/arborist/build-ideal-tree.js TAP force a new mkdirp (but not semver major) > must match snapshot 1`] = `
 ArboristNode {
   "children": Map {

test/arborist/build-ideal-tree.js

@@ -2324,3 +2324,22 @@ t.test('do not fail if root peerDep looser than meta peerDep', async t => {
   const path = resolve(fixtures, 'test-peer-looser-than-dev')
   t.matchSnapshot(await printIdeal(path))
 })
+
+t.test('adding existing dep with updateable version in package.json', async t => {
+  const path = t.testdir({
+    node_modules: {
+      lodash: {
+        'package.json': JSON.stringify({
+          version: '3.9.1'
+        })
+      }
+    },
+    'package.json': JSON.stringify({
+      devDependencies: {
+        lodash: '^3.9.1'
+      },
+    })
+  })
+
+  t.matchSnapshot(await printIdeal(path, { add: ['lodash'] }))
+})