misc/syntax/Syntax.in: fix regex for Meson syntax.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

misc/syntax/Syntax.in

@@ -70,7 +70,7 @@ include makefile.syntax
 file (CMakeLists.txt|.\*.cmake)$ CMake
 include cmake.syntax
 
-file meson.build$ Meson\sBuild\sFile
+file meson\\.build$ Meson\sBuild\sFile
 include meson.syntax
 
 file ..\*\\.(?i:pas|dpr|inc)$ Pascal\sProgram