fix: code looks not good at small sreen (close: #350)

Author: ulivz

lib/default-theme/styles/code.styl

@@ -16,8 +16,6 @@
     border-radius 6px
     padding 1.25rem 1.5rem
     margin 0.85rem 0
-    white-space pre-wrap
-    word-break break-word
     overflow auto
     position relative
     code