added code to remove empty space that was producing an error: Cropping e...

Hi,

I was receiving this error:

TypeError: Cannot read property 'geometry' of undefined
at null.callback (/home/patison/node_modules/imagemagick/imagemagick.js:155:26)
at Accumulator.finish (/home/patison/node_modules/imagemagick/imagemagick.js:60:55)
at ChildProcess. (/home/patison/node_modules/imagemagick/imagemagick.js:85:11)
at ChildProcess.EventEmitter.emit (events.js:91:17)
at Process._handle.onexit (child_process.js:674:10)

The problem was the spaces in front of the output file that the method was parsing. Fixed now.