Make sure that cmake generate build files in current dir (#194)

This should fix the `Error: could not load cache` BUG.

If there are already generated build files in the project directory,
then if you execute the command `cmake path/project` in
`$OUT_DIR/build`, cmake will not generate new build files in the
`$OUT_DIR/build` directory.

So `-B .` is needed.
https://cmake.org/cmake/help/latest/manual/cmake.1.html#cmdoption-cmake-B

Example:

```sh
cd /path/to/project
cmake .         
# output `Build files have been written to: /path/to/project`
cd /path/to/build && cmake /path/to/project
# we expect the build files will be generated at current dir (/path/to/build)
# but unfortunately get `Build files have been written to: /path/to/project`
cd /path/to/build && cmake /path/to/project -B .  
# output `Build files have been written to: /path/to/build`, that is right!
```

Infomation:
```
cmake --version
cmake version 3.27.7

CMake suite maintained and supported by Kitware (kitware.com/cmake).
```

Author: meowtec

src/lib.rs

@@ -585,6 +585,9 @@ impl Config {
         }
 
         cmd.arg(&self.path).current_dir(&build_dir);
+
+        cmd.arg("-B").arg(&build_dir);
+
         let mut is_ninja = false;
         if let Some(ref generator) = generator {
             is_ninja = generator.to_string_lossy().contains("Ninja");