CONTRIBUTORS: adds Magnus Hiie
CONTRIBUTORS: adds Magnus Hiie

From CL: https://code-review.googlesource.com/#/c/8030/

Change-Id: If52d97594641e2c1752fc34ff1440cf3771dcc4c
Reviewed-on: https://code-review.googlesource.com/10432
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Reviewed-by: Magnus Hiie <5cf7fd96b4d3e80fb3175945467acd738bf2e781@gmail.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go