Update version in case no config.h is being used

src/core.c

@@ -108,7 +108,7 @@
 #if !defined(EXTERNAL_CONFIG_FLAGS)
     #include "config.h"         // Defines module configuration flags
 #else
-    #define RAYLIB_VERSION  "2.5"
+    #define RAYLIB_VERSION  "2.6-dev"
 #endif
 
 #if (defined(__linux__) || defined(PLATFORM_WEB)) && _POSIX_C_SOURCE < 199309L