"font-lock-syntactic-keywords -> syntax-propertize-function"

I tried byte-compiling julia-mode.el to make it load faster. However, in emacs 24.3.1, the function `font-lock-syntactic-keywords` is marked as obsolete. The compiler gave a warning:
```
julia-mode.el:431:15:Warning: `font-lock-syntactic-keywords' is an obsolete
    variable (as of 24.1); use `syntax-propertize-function' instead.
```
So I changed it to `syntax-propertize-function`. 
The warning message no longer appears when I byte-compile.