Keeping the @libav.js namespace cleaner

... by naming variants @libav.js/variant-<var> instead of
@libav.js/<var>.

package-one-variant.json

@@ -1,5 +1,5 @@
 {
-  "name": "@libav.js/@VARIANT",
+  "name": "@libav.js/variant-@VARIANT",
   "version": "@VER",
   "description": "A compilation of the libraries associated with handling audio and video in ffmpeg—libavformat, libavcodec, libavfilter, libavutil and libswresample—for WebAssembly and asm.js, and thus the web.",
   "main": "dist/libav-@VERSION-@VARIANT.js",