fix gaugefix!

Author: AFeuerpfeil

src/states/ortho.jl

@@ -12,7 +12,7 @@ Algorithm for bringing an `InfiniteMPS` into the left-canonical form.
 
 $(TYPEDFIELDS)
 """
-@kwdef struct LeftCanonical{B <: DefaultBackend, A} <: Algorithm
+@kwdef struct LeftCanonical{B <: AbstractBackend, A} <: Algorithm
     "tolerance for convergence criterium"
     tol::Float64 = Defaults.tolgauge
     "maximal amount of iterations"
@@ -40,7 +40,7 @@ Algorithm for bringing an `InfiniteMPS` into the right-canonical form.
 
 $(TYPEDFIELDS)
 """
-@kwdef struct RightCanonical{B <: DefaultBackend, A} <: Algorithm
+@kwdef struct RightCanonical{B <: AbstractBackend, A} <: Algorithm
     "tolerance for convergence criterium"
     tol::Float64 = Defaults.tolgauge
     "maximal amount of iterations"