Comment typo.

Author: garydgregory

src/main/java/org/apache/commons/io/FileSystemUtils.java

@@ -507,7 +507,7 @@ List<String> performCommand(final String[] cmdAttribs, final int max, final Dura
             ThreadMonitor.stop(monitor);
 
             if (proc.exitValue() != 0) {
-                // os command problem, throw exception
+                // OS command problem, throw exception
                 throw new IOException(
                         "Command line returned OS error code '" + proc.exitValue() +
                         "' for command " + Arrays.asList(cmdAttribs));