Operation's steps are duplicated after the Operation class has been reloaded

Operation classes after reloading in the browser keep previously defined steps.

Example:
I started from a file with the following code:
```
class TestOperation < Hyperstack::Operation
step { puts "#{self} first step" }
end
```
and after the execution of the `TestOperation.run` I got:
```
# first step
```

Then I update the file having changed the step:
```
class TestOperation < Hyperstack::Operation
step { puts "#{self} new first step" }
end
```
and after the hotloader reloaded the file I executed `TestOperation.run` and got:
```
# first step
# new first step
```
while expected output should contain only the second line
```
# new first step
```

Hyperstack: branch [c0f18b0] / 1.0.alpha1.5.
Opal: 0.11.4
Browsers: Firefox 66.0.3 (64-bit), Chrome 79.0.3945.130 (Official Build) (64-bit)