fix: incorrect host when running tests

As noted in #493 (comment),
the recorded `http-data` in `src/tests` expects "http://alexcrichton-test.s3.amazonaws.com".
But, as the `S3_REGION` env var is loaded as `Some("")`,
it matches wrong leading to wrong host "http://alexcrichton-test-.s3.amazonaws.com".
This fixes it by handling match when region is empty.

Author: venkatagiri

src/s3/lib.rs

@@ -99,7 +99,8 @@ impl Bucket {
     pub fn host(&self) -> String {
         format!("{}.s3{}.amazonaws.com", self.name,
                 match self.region {
-                    Some(ref r) => format!("-{}", r),
+                    Some(ref r) if r != "" => format!("-{}", r),
+                    Some(_) => String::new(),
                     None => String::new(),
                 })
     }