docs: fix missing backtick
@@ -1738,7 +1738,7 @@ tests. It has the following methods.
- `set(varname, value)` sets environment variable in the first
argument to the value in the second argument, e.g.
- `env.set('FOO', 'BAR') sets envvar`FOO`to value`BAR\`
+ `env.set('FOO', 'BAR')` sets envvar `FOO` to value `BAR`
### `external library` object
