fix(theme-default): break long links on overflow (close #266) (#273)

Author: jiazengp

packages/@vuepress/theme-default/src/client/styles/normalize.scss

@@ -18,6 +18,7 @@ a {
   font-weight: 500;
   color: var(--c-text-accent);
   text-decoration: none;
+  overflow-wrap: break-word;
 }
 
 p a code {