chore: add missing probability keyword to stats/base/dists/uniform/mgf

Adds the `probability` keyword to `package.json` so `mgf` matches the keyword convention used by the other 13 sibling packages in `@stdlib/stats/base/dists/uniform` (93% conformance). Keyword is inserted between `dist` and `mgf` to match the ordering used by the other distribution-function packages (`cdf`, `pdf`, `logcdf`, `logpdf`, `quantile`).

Author: claude

lib/node_modules/@stdlib/stats/base/dists/uniform/mgf/package.json

@@ -58,6 +58,7 @@
     "stats",
     "distribution",
     "dist",
+    "probability",
     "mgf",
     "generating functions",
     "moments",