travis; node 11 (stable) has issues, use latest LTS version only

MikeRalphson · MikeRalphson · commit 75555a0dcf9e · 2019-04-30T10:28:07.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 sudo: false
 language: node_js
 node_js:
-  - "node"
+  - "lts/*"
 script:
   - node node_modules/mdv/mdv versions/3.*.md
