Add to specify npm version

docs/build.md

@@ -43,6 +43,8 @@ You can build the program by using `grunt`. However, we don't recommend this bec
 
 So, we've prepared a separate script which just makes an executable file.
 
+This build doesn't work on npm v5.3.0. So you need to use v5.2.0 when you build it.
+
 ```
 grunt pre-build
 ```

docs/jp/build.md

@@ -37,6 +37,8 @@ Gruntを使います。
 
 それで、実行ファイルを作るスクリプトを用意しておきました。
 
+このビルドはnpm v5.3.0では動かないのでv5.2.0で動かす必要があります。
+
 ```
 grunt pre-build
 ```

docs/ko/build.md

@@ -37,6 +37,8 @@ yarn run hot
 
 그래서, 실행파일만을 만드는 스크립트를 준비해 뒀습니다.
 
+This build doesn't work on npm v5.3.0. So you need to use v5.2.0 when you build it.
+
 ```
 grunt pre-build
 ```

docs/ru/build.md

@@ -43,6 +43,8 @@ $ yarn run dev-start
 
 Мы подготовили отдельный скрипт, который просто создает исполняемый файл:
 
+This build doesn't work on npm v5.3.0. So you need to use v5.2.0 when you build it.
+
 ```
 grunt pre-build
 ```