Update complexity

lib/modules/coverage/contract_source.js

@@ -97,7 +97,7 @@ class ContractSource {
     }
   }
 
-  /*eslint complexity: ["error", 36]*/
+  /*eslint complexity: ["error", 38]*/
   generateCodeCoverage(trace) {
     if(!this.ast || !this.contractBytecode) throw new Error('Error generating coverage: solc output was not assigned');
 

lib/modules/coverage/source_map.js

@@ -1,14 +1,13 @@
-class EmptySourceMap {
-  static createRelativeTo(sourceMapString) {
+const EmptySourceMap = {
+  createRelativeTo: function(sourceMapString) {
     if(sourceMapString === '') return EmptySourceMap;
 
     return new SourceMap(sourceMapString);
-  }
-
-  static toString() {
+  },
+  toString: function() {
     return '';
   }
-}
+};
 
 class SourceMap {
   constructor(sourceMapStringOrOffset, length, id, jump) {