Update spelling in comment in regexp.h

Author: pjcj

regexp.h

@@ -157,7 +157,7 @@ typedef struct regexp {
        the distinction between physical and logical capture buffers */
     U32 nparens;                    /* physical number of capture buffers */
     U32 logical_nparens;            /* logical_number of capture buffers */
-    I32 *logical_to_parno;          /* map logical parno to first physcial */
+    I32 *logical_to_parno;          /* map logical parno to first physical */
     I32 *parno_to_logical;          /* map every physical parno to logical */
     I32 *parno_to_logical_next;     /* map every physical parno to the next
                                        physical with the same logical id */