fix vaules in addrkVar and tokenVar UI (#298)

Author: dshvedchenko

src/main/resources/com/datapipe/jenkins/vault/credentials/VaultTokenCredentialBinding/config-variables.jelly

@@ -1,10 +1,10 @@
 <?jelly escape-by-default='true'?>
 <j:jelly xmlns:j="jelly:core" xmlns:f="/lib/form">
   <f:entry title="${%Vault Address Variable}" field="addrVariable">
-    <f:textbox value="VAULT_ADDR"/>
+    <f:textbox default="VAULT_ADDR"/>
   </f:entry>
   <f:entry title="${%Vault Token Variable}" field="tokenVariable">
-    <f:textbox value="VAULT_TOKEN"/>
+    <f:textbox default="VAULT_TOKEN"/>
   </f:entry>
   <f:entry title="${%Vault Address}" field="vaultAddr">
     <f:textbox/>