Correct Maven XSD Location

Currently used XSD location is legacy and results in a redirect.  Switch
to the redirected location.
diff --git a/slf4j-nop/pom.xml b/slf4j-nop/pom.xml
index de3f9b6..e539642 100644
--- a/slf4j-nop/pom.xml
+++ b/slf4j-nop/pom.xml
@@ -1,7 +1,7 @@
 <project
         xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 
   <parent>
     <groupId>org.slf4j</groupId>