Revert Cobertura DTD location change - cont.

http://cobertura.sourceforge.net/xml/coverage-04.dtd does not accept "complexity" attribute for <method> elements. Weird, there are two different versions of "coverage-04.dtd" available, with and without this attribute (compare http://cobertura.sourceforge.net/xml/coverage-04.dtd with https://raw.githubusercontent.com/cobertura/cobertura/master/cobertura/src/site/htdocs/xml/coverage-04.dtd).

I asked the question about this [here](cobertura/cobertura#270 (comment)) and [here](http://sourceforge.net/p/cobertura/mailman/message/34796641/).

Author: gslowikowski

scalac-scoverage-plugin/src/main/scala/scoverage/report/CoberturaXmlWriter.scala

@@ -25,8 +25,7 @@ class CoberturaXmlWriter(sourceDirectories: Seq[File], outputDir: File) extends
     <method name={method.name}
             signature="()V"
             line-rate={format(method.statementCoverage)}
-            branch-rate={format(method.branchCoverage)}
-            complexity="0">
+            branch-rate={format(method.branchCoverage)}>
       <lines>
         {method.statements.map(stmt =>
           <line