IOS crash

[liangxiwei]

Please make sure you are testing with the latest release of html2canvas.
Old versions are not supported and issues reported for them will be closed.

Please follow the general troubleshooting steps first:

• You are using the latest version
• You are testing using the non-minified version of html2canvas and checked any potential issues reported in the console

Bug reports:

the DocumentCloner.cloneNode make browser crash and reload. because the documentElement has more child node and the cloneNode call stack overflow. need make cloneNode function not recursion.

Specifications:

• html2canvas version tested with:
• Browser & version:
• Operating system: IOS wechat browser