Ensure Node.js 10 and 12 can use file-based detection methods (#30)

The requirement to provide `fs.close` with a callback was optional in Node.js 8,
then mandatory in Node.js 10 and 12, then optional from Node.js 14 onwards.

The error was caught and swallowed so users should not have noticed this.

Author: fastman

lib/filesystem.js

@@ -37,7 +37,7 @@ const readFile = (path) => new Promise((resolve, reject) => {
       const buffer = Buffer.alloc(MAX_LENGTH);
       fs.read(fd, buffer, 0, MAX_LENGTH, 0, (_, bytesRead) => {
         resolve(buffer.subarray(0, bytesRead));
-        fs.close(fd);
+        fs.close(fd, () => {});
       });
     }
   });