Adapt to changes in Gerrit core

The definition of the regular expression for a user name was moved from
the Account class into the ExternalId class.

Change-Id: Ib97e2f4201f7c021f935cf098fd4c03cfa5138b3
Signed-off-by: Edwin Kempin <ekempin@google.com>

src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
index 7077481..78c7051 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/singleusergroup/SingleUserGroup.java
@@ -30,6 +30,7 @@
 import com.google.gerrit.server.account.AbstractGroupBackend;
 import com.google.gerrit.server.account.AccountCache;
 import com.google.gerrit.server.account.AccountState;
+import com.google.gerrit.server.account.ExternalId;
 import com.google.gerrit.server.account.GroupBackend;
 import com.google.gerrit.server.account.GroupMembership;
 import com.google.gerrit.server.account.ListGroupMembership;
@@ -104,7 +105,7 @@
     AccountState state;
     if (ident.matches(ACCOUNT_ID_PATTERN)) {
       state = accountCache.get(new Account.Id(Integer.parseInt(ident)));
-    } else if (ident.matches(Account.USER_NAME_PATTERN)) {
+    } else if (ident.matches(ExternalId.USER_NAME_PATTERN_REGEX)) {
       state = accountCache.getByUsername(ident);
     } else {
       return null;