[Wave Size Range] Renumber spec (#162)

Miscommunication left this with an explicit number and circumstances put
it in before the one currently (also inappropriately) tentatively
numbered 13. This renumbers it to 13 to be sequential.

What I should have done was create it as NNNN- until just before
merging. That's what I'll do in the future.

proposals/0014-wave-size-range.md → proposals/0013-wave-size-range.md

@@ -1,6 +1,6 @@
 # Wave Size Range
 
-* Proposal: [0014](0014-wave-size-range.md)
+* Proposal: [0013](0013-wave-size-range.md)
 * Author(s): [Greg Roth](https://github.com/pow2clk)
 * Sponsor: [Greg Roth](https://github.com/pow2clk)
 * Status: **Under Consideration**