Add scale factor option (#72)

mermaid-cli includes a scale factor (`-s`) option.
Allow to configure it with `scale` option or `MERMAID_FILTER_SCALE`
environment variable.

Co-authored-by: Raghu <raghur@users.noreply.github.com>

index.js

@@ -33,6 +33,7 @@ function mermaid(type, value, format, meta) {
         background: process.env.MERMAID_FILTER_BACKROUND || 'white',
         caption: process.env.MERMAID_FILTER_CAPTION || '',
         filename: process.env.MERMAID_FILTER_FILENAME || '',
+        scale: process.env.MERMAID_FILTER_SCALE || 1,
         imageClass: process.env.MERMAID_FILTER_IMAGE_CLASS || ''
     };
     var configFile = path.join(folder, ".mermaid-config.json")
@@ -78,7 +79,7 @@ function mermaid(type, value, format, meta) {
 
     var savePath = tmpfileObj.name + "." + options.format
     var newPath = path.join(outdir, `${options.filename}.${options.format}`);
-    var fullCmd = `${cmd}  ${confFileOpts} ${puppeteerOpts} -w ${options.width} -f -i ${tmpfileObj.name} -t ${options.theme} -b ${options.background} -o ${savePath}`
+    var fullCmd = `${cmd}  ${confFileOpts} ${puppeteerOpts} -w ${options.width} -s ${options.scale} -f -i ${tmpfileObj.name} -t ${options.theme} -b ${options.background} -o ${savePath}`
     // console.log(fullCmd, savePath)
     exec(fullCmd);
     //console.log(oldPath, newPath);