Merge pull request #144 from cupro29/fix/document

fix the second sample of modint

Author: yosupo06

document_en/modint.md

@@ -35,6 +35,7 @@ If the mod is not fixed, you can use `modint` as follows.
 #include <iostream>
 
 using namespace std;
+using namespace atcoder;
 
 using mint = modint;
 // or: typedef modint mint;

document_ja/modint.md

@@ -35,6 +35,7 @@ modがfixedでない場合は、`modint` を使用し以下のように書けま
 #include <iostream>
 
 using namespace std;
+using namespace atcoder;
 
 using mint = modint;
 // or: typedef modint mint;