fix: inconsistency in rockspec

Fixes the following discrepancy between the file name and the version:
```
Error: Inconsistency between rockspec filename (rest.nvim-scm-1.rockspec) and its contents (rest.nvim-0.1-2.rockspec).
```

rest.nvim-scm-1.rockspec → rest.nvim-scm-3.rockspec

@@ -1,4 +1,4 @@
-local MAJOR, REV = "0.1", "-2"
+local MAJOR, REV = "scm", "-3"
 rockspec_format = "3.0"
 package = "rest.nvim"
 version = MAJOR .. REV