Bump reveal.js from 3.6.0 to 3.9.2 in /2019-02-01-europandas

Bumps [reveal.js](https://github.com/hakimel/reveal.js) from 3.6.0 to 3.9.2.
- [Release notes](https://github.com/hakimel/reveal.js/releases)
- [Commits](hakimel/reveal.js@3.6.0...3.9.2)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Diff for: 2019-02-01-europandas/package-lock.json

@@ -11,7 +11,7 @@
   "license": "BSD",
   "dependencies": {
     "genericons": "^1.0.1",
-    "reveal.js": "^3.4.1"
+    "reveal.js": "^3.9.2"
   },
   "devDependencies": {
     "cpx": "^1.5.0"