PARQUET-954: Use Brotli 0.6 release

Author: Uwe L. Korn <uwe@apache.org>

Closes #302 from xhochy/PARQUET-954 and squashes the following commits:

b68a10a [Uwe L. Korn] Use Brotli 0.6 release
diff --git a/cmake_modules/ThirdpartyToolchain.cmake b/cmake_modules/ThirdpartyToolchain.cmake
index f573cf4..15a20bd 100644
--- a/cmake_modules/ThirdpartyToolchain.cmake
+++ b/cmake_modules/ThirdpartyToolchain.cmake
@@ -20,8 +20,7 @@
 set(SNAPPY_VERSION "1.1.3")
 set(THRIFT_VERSION "0.10.0")
 
-# Brotli 0.5.2 does not install headers/libraries yet, but 0.6.0.dev does
-set(BROTLI_VERSION "5db62dcc9d386579609540cdf8869e95ad334bbd")
+set(BROTLI_VERSION "v0.6.0")
 
 # find boost headers and libs
 set(Boost_DEBUG TRUE)