libsysprof-capture: Use an internal header in writer-cat.c

This makes no functional difference, but does tidy up the code style a
bit. All other internal headers are included using quotes in other
files.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Helps: #40

src/libsysprof-capture/sysprof-capture-writer-cat.c

@@ -61,9 +61,9 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <sysprof-capture.h>
 #include <unistd.h>
 
+#include "sysprof-capture.h"
 #include "sysprof-macros-internal.h"
 
 typedef struct