[Tails-dev] Small typo in the contributers doc

Hi, this fixes a small typo in the "Building a Tails image" documentation.

diff --git a/wiki/src/contribute/build.mdwn b/wiki/src/contribute/build.mdwn
index ed0a4f0..f22071e 100644
--- a/wiki/src/contribute/build.mdwn
+++ b/wiki/src/contribute/build.mdwn
@@ -30,7 +30,7 @@ For details how Vagrant is setup, see its
## Installing the dependencies in Debian

If you run Debian Jessie, you must install a few dependencies from
-Debian Stretch, and one of Tails' repos until [!debbug 823395]] is fixed:
+Debian Stretch, and one of Tails' repos until [[!debbug 823395]] is fixed:

     sudo tee /etc/apt/sources.list.d/stretch.list <<EOF
     deb http://ftp.us.debian.org/debian/ stretch main

Cheers!
diff --git a/wiki/src/contribute/build.mdwn b/wiki/src/contribute/build.mdwn
index ed0a4f0..f22071e 100644
--- a/wiki/src/contribute/build.mdwn
+++ b/wiki/src/contribute/build.mdwn
@@ -30,7 +30,7 @@ For details how Vagrant is setup, see its
## Installing the dependencies in Debian

If you run Debian Jessie, you must install a few dependencies from
-Debian Stretch, and one of Tails' repos until [!debbug 823395]] is fixed:
+Debian Stretch, and one of Tails' repos until [[!debbug 823395]] is fixed:

     sudo tee /etc/apt/sources.list.d/stretch.list <<EOF
     deb http://ftp.us.debian.org/debian/ stretch main