PSO seens cannot treat equal constraints

Hi, it seems the equation in PSO doesn't work effectively, this is the code:

```
def demo_func(x):
x1, x2 = x
return -20 * np.exp(-0.2 * np.sqrt(0.5 * (x1 ** 2 + x2 ** 2))) - np.exp(
0.5 * (np.cos(2 * np.pi * x1) + np.cos(2 * np.pi * x2))) + 20 + np.e

# I add this equation
constraint_eq = [
lambda x: 2 - x[0] - x[1],
]

constraint_ueq = (
lambda x: (x[0] - 1) ** 2 + (x[1] - 0) ** 2 - 0.5 ** 2
,
)

max_iter = 50
pso = PSO(func=demo_func, n_dim=2, pop=40, max_iter=max_iter, lb=[-2, -2], ub=[2, 2],
constraint_eq=constraint_eq,
constraint_ueq=constraint_ueq)
pso.record_mode = True
pso.run()
print('best_x is ', pso.gbest_x, 'best_y is', pso.gbest_y)

# but it seems not effective
print('the sume of x:', sum(pso.gbest_x))
```

the output is
```
best_x is [ 9.51948501e-01 -3.04008149e-04] best_y is [2.57993123]
the sume of x: 0.9516444926553026
```

we can see that `x[0] + x[1] = 2` doesn't work, is there any problem with my code?