Add missing vendor files to make godeps happy

vendor/github.com/prometheus/client_golang/AUTHORS.md

@@ -0,0 +1,18 @@
+The Prometheus project was started by Matt T. Proud (emeritus) and
+Julius Volz in 2012.
+
+Maintainers of this repository:
+
+* Björn Rabenstein <beorn@soundcloud.com>
+
+The following individuals have contributed code to this repository
+(listed in alphabetical order):
+
+* Bernerd Schaefer <bj.schaefer@gmail.com>
+* Björn Rabenstein <beorn@soundcloud.com>
+* Daniel Bornkessel <daniel@soundcloud.com>
+* Jeff Younker <jeff@drinktomi.com>
+* Julius Volz <julius@soundcloud.com>
+* Matt T. Proud <matt.proud@gmail.com>
+* Tobias Schmidt <ts@soundcloud.com>
+

vendor/github.com/prometheus/client_model/AUTHORS.md

@@ -0,0 +1,13 @@
+The Prometheus project was started by Matt T. Proud (emeritus) and
+Julius Volz in 2012.
+
+Maintainers of this repository:
+
+* Björn Rabenstein <beorn@soundcloud.com>
+
+The following individuals have contributed code to this repository
+(listed in alphabetical order):
+
+* Björn Rabenstein <beorn@soundcloud.com>
+* Matt T. Proud <matt.proud@gmail.com>
+* Tobias Schmidt <ts@soundcloud.com>

vendor/github.com/prometheus/common/AUTHORS.md

@@ -0,0 +1,11 @@
+Maintainers of this repository:
+
+* Fabian Reinartz <fabian@soundcloud.com>
+
+The following individuals have contributed code to this repository
+(listed in alphabetical order):
+
+* Björn Rabenstein <beorn@soundcloud.com>
+* Fabian Reinartz <fabian@soundcloud.com>
+* Julius Volz <julius@soundcloud.com>
+* Miguel Molina <hi@mvader.me>