Fixed typo in erlc documentation

* Documentation is inconsistent with erlc arguments [1]
* Made the change s/WError/Werror/

```
$ erlc --help 2>&1 | grep 'W[eE]'
-Werror        make all warnings into errors
```

[1] https://www.erlang.org/doc/apps/erts/erlc_cmd.html#generally-useful-flags

erts/doc/references/erlc_cmd.md

@@ -63,7 +63,7 @@ The following flags are supported:
   containing tuples and lists must be quoted. Terms containing spaces must be
   quoted on all platforms.
 
-- **`-WError`** - Makes all warnings into errors.
+- **`-Werror`** - Makes all warnings into errors.
 
 - **`-W<Number>`** - Sets warning level to `Number`. Defaults to `1`. To turn
   off warnings, use `-W0`.