fix: date parsing throws IllegalArgumentException.

When minio-java is used in system running with different locale than
English, date parsing fails with IllegalArgumentException.  This patch
fixes the issue by setting the locale to English for all date formats.

Fixes minio#411

src/main/java/io/minio/DateFormat.java

@@ -16,6 +16,8 @@
 
 package io.minio;
 
+import java.util.Locale;
+
 import org.joda.time.format.DateTimeFormat;
 import org.joda.time.format.DateTimeFormatter;
 
@@ -25,17 +27,18 @@
  */
 public class DateFormat {
   public static final DateTimeFormatter AMZ_DATE_FORMAT =
-      DateTimeFormat.forPattern("yyyyMMdd'T'HHmmss'Z'").withZoneUTC();
+      DateTimeFormat.forPattern("yyyyMMdd'T'HHmmss'Z'").withZoneUTC().withLocale(Locale.ENGLISH);
 
   public static final DateTimeFormatter EXPIRATION_DATE_FORMAT =
-      DateTimeFormat.forPattern("yyyy-MM-dd'T'HH':'mm':'ss'.'SSS'Z'").withZoneUTC();
+      DateTimeFormat.forPattern("yyyy-MM-dd'T'HH':'mm':'ss'.'SSS'Z'").withZoneUTC().withLocale(Locale.ENGLISH);
 
   public static final DateTimeFormatter RESPONSE_DATE_FORMAT = EXPIRATION_DATE_FORMAT;
 
-  public static final DateTimeFormatter SIGNER_DATE_FORMAT = DateTimeFormat.forPattern("yyyyMMdd").withZoneUTC();
+  public static final DateTimeFormatter SIGNER_DATE_FORMAT = 
+      DateTimeFormat.forPattern("yyyyMMdd").withZoneUTC().withLocale(Locale.ENGLISH);
 
   public static final DateTimeFormatter HTTP_HEADER_DATE_FORMAT =
-      DateTimeFormat.forPattern("EEE',' dd MMM yyyy HH':'mm':'ss zzz").withZoneUTC();
+      DateTimeFormat.forPattern("EEE',' dd MMM yyyy HH':'mm':'ss zzz").withZoneUTC().withLocale(Locale.ENGLISH);
 
   private DateFormat() {}
 }