gplazma2-oidc-te: fix invalid initialization of plugin

Motivation:
The META-INF/gplazma-plugins.xml must point to the correct class name,
otherwise we get:

Unable register new plugin: Class org.dcache.gplazma.plugins.tokenx.TokenExchange could not be found.

Modification:
Fix the class name in gplazma-plugins.xml

Result:
no error on start (and working plugin :) )

Acked-by: Paul Millar
Target: master, 10.1
Require-book: no
Require-notes: yes
(cherry picked from commit bb836be)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>

modules/gplazma2-oidc-te/src/main/resources/META-INF/gplazma-plugins.xml

@@ -1,6 +1,6 @@
 <plugins>
     <plugin>
         <name>oidc-te</name>
-        <class>org.dcache.gplazma.plugins.tokenx.TokenExchange</class>
+        <class>org.dcache.gplazma.tokenx.TokenExchange</class>
     </plugin>
 </plugins>