PARQUET-1146: Add macOS-compatible sha512sum call to release verify script

Author: Korn, Uwe <Uwe.Korn@blue-yonder.com>

Closes #414 from xhochy/PARQUET-1146 and squashes the following commits:

74821cc [Korn, Uwe] PARQUET-1146: Add macOS-compatible sha512sum call to release verify script
diff --git a/dev/release/verify-release-candidate b/dev/release/verify-release-candidate
index 0310397..8555b8a 100755
--- a/dev/release/verify-release-candidate
+++ b/dev/release/verify-release-candidate
@@ -43,7 +43,11 @@
   download_rc_file ${dist_name}.tar.gz.sha512
   gpg --verify ${dist_name}.tar.gz.asc ${dist_name}.tar.gz
   gpg --print-md MD5 ${dist_name}.tar.gz | diff - ${dist_name}.tar.gz.md5
-  sha512sum ${dist_name}.tar.gz | diff - ${dist_name}.tar.gz.sha512
+  if [ "$(uname)" == "Darwin" ]; then
+    shasum -a 512 ${dist_name}.tar.gz | diff - ${dist_name}.tar.gz.sha512
+  else
+    sha512sum ${dist_name}.tar.gz | diff - ${dist_name}.tar.gz.sha512
+  fi
 }
 
 run_tests() {