create fallback gtest subproject dependency

Signed-off-by: Zane Shelley <zshelle@us.ibm.com>
Change-Id: I6b0ce32242a0a74b56f4a163cfb3a1e15fe8a7ee
diff --git a/meson.build b/meson.build
index 9837e17..75d56df 100644
--- a/meson.build
+++ b/meson.build
@@ -1,6 +1,6 @@
 # See README.md for details.
 project('openpower-hw-diags', 'cpp',
-        version: '0.1', meson_version: '>=0.50.0',
+        version: '0.1', meson_version: '>=0.51.0',
         default_options: [
           'warning_level=3',
           'werror=true',