Merge pull request #132 from kdnakt/translate-conversion

Translate untranslated line in conversion.md

Author: dalance

src/conversion.md

@@ -3,7 +3,10 @@
 -->
 # 型変換
 
+<!--
 Primitive types can be converted to each other through [casting].
+-->
+プリミティブ型同士は[キャスティング][casting]を用いて変換できます。
 
 <!--
 Rust addresses conversion between custom types (i.e., `struct` and `enum`)