fix: cover button style, fixed #670, fixed #665 (#675)

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A temporary solution, I will refactor this part of the code in the next major version.

Author: QingWei-Li

src/core/render/index.js

@@ -198,6 +198,17 @@ export function renderMixin(proto) {
       html = html.replace(m[0], '')
     }
 
+    // XXX: A Workaround
+    html = html
+      .split('\n')
+      .map(part => {
+        if (/^<a/.test(part)) {
+          return part.replace('<a', '<a data-button')
+        }
+        return part
+      })
+      .join('\n')
+
     this._renderTo('.cover-main', html)
     sticky()
   }

src/themes/basic/_coverpage.styl

@@ -61,7 +61,7 @@ section.cover
     max-width 500px
     padding 0
 
-  .cover-main > p:last-child a
+  .cover-main > a[data-button]
     border-color var(--theme-color, $color-primary)
     border-radius 2rem
     border-style solid