Add windows to travis build

.travis.yml

@@ -1,4 +1,7 @@
 language: node_js
+os:
+  - linux
+  - windows
 node_js:
   - "8"
   - "10"

lib/image-util.js

@@ -7,6 +7,7 @@ import { hasValue } from './util';
 import { exec } from 'teen_process';
 import path from 'path';
 import fs from './fs';
+import log from './logger';
 
 
 const { MIME_JPEG, MIME_PNG, MIME_BMP } = Jimp;
@@ -96,6 +97,7 @@ async function getJimpImage (data) {
  * modules that are installed globally
  *
  * @param {string} packageName - the name of the package to be required
+ * @returns {object} - the package object
  */
 async function requirePackage (packageName) {
   // see if we can get it locally
@@ -109,6 +111,7 @@ async function requirePackage (packageName) {
 
   // get the global package root
   const packageDir = path.join(globalNPMRoot, packageName);
+  log.debug(`Loading package '${packageName}' from '${packageDir}'`);
   if (!await fs.exists(packageDir)) {
     // not installed
     throw new Error(`Unable to find global '${packageName}' module`);
@@ -124,7 +127,9 @@ async function initOpenCV () {
   if (!cv) {
     try {
       cv = await requirePackage('opencv4nodejs');
-    } catch (ign) {}
+    } catch (err) {
+      log.debug(`Unable to load 'opencv4nodejs': ${err.message}`);
+    }
   }
   if (!cv) {
     throw new Error(`'opencv4nodejs' module is required to use OpenCV features. ` +