Bump lodash from 4.17.13 to 4.17.15

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.13 to 4.17.15.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](lodash/lodash@4.17.13...4.17.15)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -11,7 +11,7 @@
   },
   "dependencies": {
     "js-slang": "^0.2.6",
-    "lodash": "4.17.13"
+    "lodash": "4.17.15"
   },
   "devDependencies": {
     "@types/jest": "^24.0.13",