Update DropBox documentation

A minor change to make a couple of sentences more grammatical.
merge dev_5_0 -D org: PR 813 (Update DropBox documentation)
merge dev_5_0 -D org

Repository: openmicroscopy/ome-documentation
Excluded PRs:
  # PR 811 will-moore 'Webgateway mip 5150' (status: )
Updating c858dcf..fb7eaf8
Merged PRs (fast-forward):
  # PR 804 hflynn 'Adding example server setup page '
  # PR 808 sbesson 'Travis fix'

Merged PRs:
  # PR 813 ximenesuk 'Update DropBox documentation'

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