Update meson build requirement

Currently, we have a build type warning due to listing a requirement for
meson build version that doesn't implement features we use in our build
file. The minimum meson build version required is actually 0.50.0, so
this PR updates our meson.build file to depend on 0.50.0.
diff --git a/meson.build b/meson.build
index 106e17f..ece8aa4 100644
--- a/meson.build
+++ b/meson.build
@@ -7,7 +7,7 @@
     'cpp_std=c++11',
     'warning_level=1'],
   license : 'Public Domain',
-  meson_version : '>= 0.41.1')
+  meson_version : '>= 0.50.0')
 
 jsoncpp_ver_arr = meson.project_version().split('.')
 jsoncpp_major_version = jsoncpp_ver_arr[0]