Update map.py to fix broken urls (jsdelivr)

Changed urls to JSDelivr

Author: James Stevenson

folium/map.py

@@ -28,7 +28,7 @@
 
 _default_js = [
     ('leaflet',
-     'https://unpkg.com/leaflet@1.2.0/dist/leaflet.js'),
+     'https://cdn.jsdelivr.net/npm/leaflet@1.1.0/dist/leaflet.js'),
     ('jquery',
      'https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js'),
     ('bootstrap',
@@ -43,7 +43,7 @@
 
 _default_css = [
     ('leaflet_css',
-     'https://unpkg.com/leaflet@1.2.0/dist/leaflet.css'),
+     'https://cdn.jsdelivr.net/npm/leaflet@1.1.0/dist/leaflet.css'),
     ('bootstrap_css',
      'https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css'),
     ('bootstrap_theme_css',