bug fix

themis-common/src/main/java/com/qmth/themis/common/contanst/Constants.java

@@ -4,7 +4,7 @@ import java.nio.charset.Charset;
 
 public interface Constants {
 
-    public static final int SIGNATURE_EXPIRE_SECONDS = 15;
+    public static final int SIGNATURE_EXPIRE_SECONDS = 30;
 
     public static final int SIGNATURE_AHEAD_SECONDS = 5;