[docs] Fix LaTeX alignment in example of VectorNonlinearOracle docstring (#2886)

Author: franckgaga

src/sets.jl

@@ -2741,10 +2741,10 @@ Any mix of lower and upper-triangular indices is valid. Elements `(i, j)` and
 
 To model the set:
 ```math
-\\begin{align}
-0 \\le & x^2                   \\le 1
-0 \\le & y^2 + x \\cdot z^3 - w \\le 0
-\\end{align}
+\\begin{aligned}
+0 &\\le x^2                    & \\le 1 \\\\
+0 &\\le y^2 + x \\cdot z^3 - w & \\le 0
+\\end{aligned}
 ```
 do
 ```jldoctest