Update examples/heisenberg/main.jl

Co-authored-by: Lukas Devos <ldevos98@gmail.com>

Author: pbrehmer

examples/heisenberg/main.jl

@@ -9,7 +9,7 @@ PEPS. To that end, we will consider the two-dimensional Heisenberg model on a sq
 H = \sum_{\langle i,j \rangle} \left ( J_x S^{x}_i S^{x}_j + J_y S^{y}_i S^{y}_j + J_z S^{z}_i S^{z}_j \right )
 ```
 
-Here, we want to set $J_x=J_y=J_z=1$ where the Heisenberg model is in the antiferromagnetic
+Here, we want to set $J_x = J_y = J_z = 1$ where the Heisenberg model is in the antiferromagnetic
 regime. Due to the bipartite sublattice structure of antiferromagnetic order one needs a
 PEPS ansatz with a $2 \times 2$ unit cell. This can be circumvented by performing a unitary
 sublattice rotation on all B-sites resulting in a change of parameters to