Update main version.h to NEXT release (#9834)

Summary:
Henceforth, the version number in version.h shall reflect the
*next* version number to be tagged (to the best of our knowledge) rather
than the *previous* (unpatched) version.

The primary advantage is being able to distinguish (in source code `#if`s
or human running tools) the development version from the last released
version.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9834

Test Plan: CI

Reviewed By: ajkr

Differential Revision: D35617373

Pulled By: pdillinger

fbshipit-source-id: f3286089d17b82409e6af08e5aa9c1affefe2862

include/rocksdb/version.h

@@ -9,8 +9,10 @@
 
 #include "rocksdb/rocksdb_namespace.h"
 
+// NOTE: in 'main' development branch, this should be the *next*
+// minor or major version number planned for release.
 #define ROCKSDB_MAJOR 7
-#define ROCKSDB_MINOR 1
+#define ROCKSDB_MINOR 2
 #define ROCKSDB_PATCH 0
 
 // Do not use these. We made the mistake of declaring macros starting with