Allow capitals as first character in bucket name

Curiously Amazon permits mixed case but documents that only lowercase
letters are allowed:

https://docs.aws.amazon.com/AmazonS3/latest/dev/BucketRestrictions.html

Fixes #226.

src/main/java/org/gaul/s3proxy/S3ProxyHandler.java

@@ -128,10 +128,10 @@ public class S3ProxyHandler {
     private static final String FAKE_REQUEST_ID = "4442587FB7D0A2F9";
     private static final CharMatcher VALID_BUCKET_FIRST_CHAR =
             CharMatcher.inRange('a', 'z')
+                    .or(CharMatcher.inRange('A', 'Z'))
                     .or(CharMatcher.inRange('0', '9'));
     private static final CharMatcher VALID_BUCKET =
             VALID_BUCKET_FIRST_CHAR
-                    .or(CharMatcher.inRange('A', 'Z'))
                     .or(CharMatcher.is('.'))
                     .or(CharMatcher.is('_'))
                     .or(CharMatcher.is('-'));