[FS#977] building iw is currently failing on version.sh

[LEDE Bugs]

The following task has a new comment added:

FS#977 - building iw is currently failing on version.sh
User who did this - Stijn Tintel (stintel)

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Adding a shebang line in version.sh seems to fix it, but I have no idea why.
https://git.lede-project.org/fe3a5720
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=977#comment3507