Add locale to HttpHeaderParserTest.rfc1123Date(long millis)

There is a DateParseException when the test runs on a german system
org.apache.http.impl.cookie.DateParseException: Unable to parse the date So., 21 Sep. 2014 22:43:50 MESZ

Change-Id: I8a52af1dfc24d82f8f6157ff7d661014f1ee8d26

Author: Ralph Bergmann

tests/src/com/android/volley/toolbox/HttpHeaderParserTest.java

@@ -21,14 +21,15 @@
 import com.android.volley.Cache;
 import com.android.volley.NetworkResponse;
 
+import junit.framework.TestCase;
+
 import java.text.DateFormat;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
-import junit.framework.TestCase;
-
 @SmallTest
 public class HttpHeaderParserTest extends TestCase {
 
@@ -162,7 +163,7 @@ private void assertEqualsWithin(long expected, long value, long fudgeFactor) {
     }
 
     private static String rfc1123Date(long millis) {
-        DateFormat df = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz");
+        DateFormat df = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss zzz", Locale.ENGLISH);
         return df.format(new Date(millis));
     }