use an integer field for length

prolefeeder.py

@@ -2,7 +2,7 @@ from flask import (Flask, render_template, flash, redirect,
                    url_for, request, send_from_directory)
 from flask_bootstrap import Bootstrap
 from flask_wtf import FlaskForm
-from wtforms import DateTimeField, DecimalField, SubmitField
+from wtforms import DateTimeField, IntegerField, SubmitField
 from wtforms.validators import DataRequired, NumberRange
 
 from datetime import datetime, timedelta
@@ -21,7 +21,7 @@ Bootstrap(app)
 
 class DownloadForm(FlaskForm):
     start_time = DateTimeField('Start time', validators=[DataRequired()], id='start_time')
-    length = DecimalField('Length', validators=[DataRequired(),
+    length = IntegerField('Length', validators=[DataRequired(),
                                                 NumberRange(min=1, max=app.config['MAX_LENGTH'])])
     submit = SubmitField('Download')