Download magicleap signing certificate

[asajeffrey]

Magic Leap apps need to be signed, fortunately we have a dummy signing key.

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This change is 

[jdm]

@bors-servo r+

[bors-servo]

:pushpin: Commit 5b0a0ad has been approved by jdm

[bors-servo]

:hourglass: Testing commit 5b0a0adaeff5f89de2eaebacdbe24e8d1fe79cb4 with merge 2da70a94d5b11e06e83279e2aad4891aaa71197f...

[asajeffrey]

Yaml files are dictionaries, you can't have repeated keys, d'oh!

[CRITICAL] Rendering SLS 'base:servo-build-dependencies.mac-magicleap' failed: while constructing a mapping
  in "<unicode string>", line 20, column 3:
      cmd.run:
      ^
found conflicting ID 'cmd.run'
  in "<unicode string>", line 31, column 3:
      cmd.run:
      ^
local:
    - Rendering SLS 'base:servo-build-dependencies.mac-magicleap' failed: while constructing a mapping
        in "<unicode string>", line 20, column 3:
            cmd.run:
            ^
      found conflicting ID 'cmd.run'
        in "<unicode string>", line 31, column 3:
            cmd.run:
            ^
The command ".travis/dispatch.sh" exited with 1.

[asajeffrey]

@bors-servo r=jdm

[bors-servo]

:pushpin: Commit 5e64ca3 has been approved by jdm

[bors-servo]

:hourglass: Testing commit 5e64ca3f603a734247b33597046cfc80022d36d4 with merge 3e12b5cbd4d2d2aa1a8c7fbb27a74dcbf3707b38...

[bors-servo]

:sunny: Test successful - status-travis Approved by: jdm Pushing 3e12b5cbd4d2d2aa1a8c7fbb27a74dcbf3707b38 to master...