Change default makeinfo path

With the switch to UIOP:RUN-PROGRAM, it makes sense to default to
the one found in the path. The user can still specify a custom
location if needed.

quickref.lisp

@@ -97,7 +97,7 @@ The resulting .texi file is placed inside the release's directory, in
   (dolist (release (ql-dist:provided-releases t))
     (ql-dist:uninstall release)))
 
-(defparameter *makeinfo-path* "/usr/local/bin/makeinfo")
+(defparameter *makeinfo-path* "makeinfo")
 (defparameter *log-errors* t)
 (defparameter *remove-cache* nil)