Change plexus-utils to compile scope from provided (#65)

This is remnant from Maven2 and worked in Maven3 due
Maven3 backward compatibility layer toward Maven2. This is
getting removed in Maven 3.9.0 and 4.

Plexus Utils is now a compile scope dependency of the plugin,
because we can't expect Maven3 and 4 to provide it.

This fixes #64

pom.xml

@@ -146,6 +146,10 @@
       <groupId>com.google.guava</groupId>
       <artifactId>guava</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.codehaus.plexus</groupId>
+      <artifactId>plexus-utils</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.apache.maven</groupId>
       <artifactId>maven-core</artifactId>
@@ -161,11 +165,6 @@
       <artifactId>maven-plugin-annotations</artifactId>
       <scope>provided</scope>
     </dependency>
-    <dependency>
-      <groupId>org.codehaus.plexus</groupId>
-      <artifactId>plexus-utils</artifactId>
-      <scope>provided</scope>
-    </dependency>
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter</artifactId>