Not able to add break points on Mac

**Describe the bug**
1. Not able to add break points.

**To Reproduce**
Steps to reproduce the behavior:
My code is simple.

```
fn main() {
let a = 2;
let result = stack_only(a);
dbg!(result);
}

fn stack_only(b: i32) -> i32 {
let c = 3;
return b + c + stack_and_heap();
}

fn stack_and_heap() -> i32 {
let d = 5;
let e = Box::new(7);
return d + *e;
}
```

I fetched the file.


I click line numbers but it doesn't add line breaks.

**Please complete the following information:**
* OS: macOS v10.15.6
* gdbgui version (`gdbgui -v`): 0.14.0.0
* gdb version (`gdb -v`):
* browser [e.g. chrome, safari]: command not found: gdb ( I installed gdbgui with pipx.)
* python packages (`pip freeze`):
appdirs==1.4.4
argcomplete==1.12.0
certifi==2020.6.20
chardet==3.0.4
click==7.1.2
distlib==0.3.1
dominate==2.5.1
filelock==3.0.12
Flask==1.1.2
Flask-Bootstrap==3.3.7.1
flask-marshmallow==0.13.0
Flask-SQLAlchemy==2.4.4
Flask-WTF==0.14.3
flickrapi==2.4.0
idna==2.10
itsdangerous==1.1.0
Jinja2==2.11.2
MarkupSafe==1.1.1
marshmallow==3.7.1
marshmallow-sqlalchemy==0.23.1
numpy==1.19.1
oauthlib==3.1.0
packaging==20.4
pandas==1.1.0
pipenv==2020.8.13
pipx==0.15.5.1
PyMySQL==0.10.0
pyparsing==2.4.7
python-dateutil==2.8.1
python-dotenv==0.14.0
pytz==2020.1
requests==2.24.0
requests-oauthlib==1.3.0
requests-toolbelt==0.9.1
six==1.15.0
SQLAlchemy==1.3.19
urllib3==1.25.10
userpath==1.4.1
virtualenv==20.0.31
virtualenv-clone==0.5.4
visitor==0.1.3
Werkzeug==1.0.1
WTForms==2.3.3

The issue names no source files or tests. Start by reproducing the breakpoint-click failure in gdbgui 0.14.0.0 on macOS 10.15.6 with the supplied Rust program, and verify the gdb and browser setup. Done means identifying the cause and confirming that clicking a line number adds a breakpoint in the affected environment.

Written by the indexing model from the issue text.