Use default field length for EmailField

EmailField is already max_length=254 in Django 1.8

ref #13

coin/isp_database/models.py

@@ -61,9 +61,8 @@ class ISPInfo(SingleInstanceMixin, models.Model):
                               help_text="HTTP(S) URL of the ISP's logo")
     website = models.URLField(blank=True,
                               help_text='URL to the official website')
-    email = models.EmailField(max_length=254,
-                              help_text="Contact email address")
-    mainMailingList = models.EmailField(max_length=254, blank=True,
+    email = models.EmailField(help_text="Contact email address")
+    mainMailingList = models.EmailField(blank=True,
                                         verbose_name="main mailing list",
                                         help_text="Main public mailing-list")
     phone_number = models.CharField(max_length=25, blank=True,
@@ -97,11 +96,11 @@ class ISPInfo(SingleInstanceMixin, models.Model):
 
     # field outside of db-ffdn format:
     administrative_email = models.EmailField(
-        max_length=254, blank=True, verbose_name="contact administratif",
+        blank=True, verbose_name="contact administratif",
         help_text='Adresse email pour les contacts administratifs (ex: bureau)')
 
     support_email = models.EmailField(
-        max_length=254, blank=True, verbose_name="contact de support",
+        blank=True, verbose_name="contact de support",
         help_text="Adresse email pour les demandes de support technique")
 
     lists_url = models.URLField(