Fixed typo: conformance_test_runner should be a binary, not library.

BUILD

diff --git a/BUILD b/BUILD
index f8ad0c5..d681994 100644
--- a/BUILD
+++ b/BUILD
@@ -1091,7 +1091,7 @@
     ],
 )
 
-cc_library(
+cc_binary(
     name = "conformance_test_runner",
     srcs = ["conformance/conformance_test_main.cc"],
     deps = [