Update dependency kramdown to v2.5.0

Author: renovate[bot]

Gemfile.lock

@@ -71,8 +71,8 @@ GEM
       sass-embedded (~> 1.54)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.4.0)
-      rexml
+    kramdown (2.5.0)
+      rexml (>= 3.3.6)
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.4)
@@ -102,7 +102,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.6)
+    rexml (3.3.9)
     rouge (4.1.3)
     ruby-rc4 (0.1.5)
     ruby2_keywords (0.0.5)