fix: buble theme missing generic fallback font (#1568)

Author: sy-records

src/themes/buble.styl

@@ -101,14 +101,14 @@ $sidebar-width = 16rem
 .markdown-section code
   background-color #f9f9f9
   border-radius 3px
-  font-family Inconsolata
+  font-family Inconsolata, monospace
   padding 0.2em 0.4rem
   white-space nowrap
 
 .markdown-section pre
   background-color #f9f9f9
   border-left 2px solid #eee
-  font-family Inconsolata
+  font-family Inconsolata, monospace
   font-size 16px
   margin 0 0 1em 0
   padding 8px
@@ -159,7 +159,7 @@ $sidebar-width = 16rem
   background-color #f8f8f8
   border-radius 2px
   display block
-  font-family Inconsolata
+  font-family Inconsolata, monospace
   line-height 1.1rem
   max-width inherit
   overflow inherit