Don't create pdfmake object if browser doesn't support required APIs
Don't create pdfmake object if browser doesn't support required APIs

If you load pdfmake in IE8- you get an error on the page because it doesn't provide `Object.keys`. While I don't propose that pdfmake should support these legacy browsers (!) it would be great if simply loading the file didn't cause them to throw a Javascript error, stopping all other Javascript execution.

While it would be easy to have pdfmake included with conditional comments if it were being loaded as a single file, that isn't so easy where concatenation of libraries is used. This little change just sidesteps it.
TW-QEN/pdfmake,dennisrjohn/pdfmake,bavellone/pdfmake,dennisrjohn/pdfmake,TW-QEN/pdfmake,bavellone/pdfmake