Bump lein to 2.8.3 in Travis config

cichli · bbatsov · commit 53d770c5abfa · 2019-01-16T11:51:43.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,5 @@
 language: clojure
-lein: 2.8.1
+lein: 2.8.3
 sudo: false
 cache:
   directories:
