ios15 support

[mrkazu]

Thank you HJ29 for making this fork. It works great!
For those who needs a quick fix for ios15 support make the following changes.

in src/components/QrStream.vue
replace line 10
v-show="shouldScan"
with
:class="{ 'qrcode-stream-camera--hidden': !shouldScan }"

and add the following to the styles tag

.qrcode-stream-camera--hidden {
  visibility: hidden;
  position: absolute;
}