fix compilation with newer gtest (#514)

C++17 now.

Author: SRombauts

meson.build

@@ -1,8 +1,8 @@
 project(
     'SQLiteCpp', 'cpp',
     # SQLiteCpp supports C++11
-    # however newer versions of gtest requires C++14
-    default_options: ['cpp_std=c++14', 'warning_level=3'],
+    # however newer versions of gtest requires C++17
+    default_options: ['cpp_std=c++17', 'warning_level=3'],
     license: 'MIT',
     version: '3.3.3',
 )