Disable axe color contrast checks

These checks require a real browser environment and fail in jsdom.

Closes #147

index.js

@@ -47,11 +47,22 @@ function configureAxe (options = {}) {
 
   const { globalOptions = {}, ...runnerOptions } = options
 
+  const globalOptionOverrides = {
+    checks: [{
+      // By default, color contrast checking doesnt work in a jsdom environment.
+      // Disabled this check by default.
+      id: 'color-contrast',
+      enabled: false
+    }]
+  };
+
   // Set the global configuration for
   // axe-core 
   // https://github.com/dequelabs/axe-core/blob/develop/doc/API.md#api-name-axeconfigure 
-  axeCore.configure(globalOptions)
-
+  axeCore.configure(Object.assign({},
+    globalOptions,
+    globalOptionOverrides
+  ))
 
   /**
    * Small wrapper for axe-core#run that enables promises (required for Jest),