Fix deprecated werkzeug import

Close: #1830
Signed-off-by: Nicolas Gelot <nicolas.gelot@e.email>

requirements.txt

 certifi==2019.3.9
 babel==2.7.0
-flask-babel==0.12.2
+flask-babel==1.0.0
 flask==1.0.2
 idna==2.8
 jinja2==2.10.1

searx/webapp.py

@@ -47,7 +47,7 @@ except:
     from html import escape
 from datetime import datetime, timedelta
 from time import time
-from werkzeug.contrib.fixers import ProxyFix
+from werkzeug.middleware.proxy_fix import ProxyFix
 from flask import (
     Flask, request, render_template, url_for, Response, make_response,
     redirect, send_from_directory