ZooniverseClient: generateAuthorizationHeader: Use the correct (UTF8)…

… encoding.

With this, the server reports a successful upload, but I don't see it yet
the uploads yet on my profile page:
http://www.galaxyzoo.org/#/profile/recents/1
Something else must be wrong. We already know that the server can report
success when the apiKey is wrong, for instance:
zooniverse/Galaxy-Zoo#184
However, in this case our Authentication header does seem to be
exactly the same as what android-galaxyzoo uses for the same login,
and that still works.

ios-galaxyzoo/client/ZooniverseClient.m

@@ -410,10 +410,10 @@ + (NSString *)getAnnotationPart:(NSInteger)sequence {
 + (NSString *)generateAuthorizationHeader:(NSString *)authName
                                authApiKey:(NSString *)authApiKey {
     NSString *str = [NSString stringWithFormat:@"%@:%@", authName, authApiKey];
-    NSData *data = [str dataUsingEncoding:NSUnicodeStringEncoding];
+    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
 
-    NSString *result = [data base64EncodedStringWithOptions:0];
-    return result;
+    NSString *encoded = [data base64EncodedStringWithOptions:0];
+    return [NSString stringWithFormat:@"Basic %@", encoded];
 }
 
 - (void)uploadClassifications {