fix deprecation warning from pytest (#3354)

gensim/matutils.py:22: DeprecationWarning: Please use `triu` from the `scipy.linalg` namespace, the `scipy.linalg.special_matrices` namespace is deprecated.
    from scipy.linalg.special_matrices import triu

gensim/matutils.py

@@ -17,9 +17,8 @@
 import numpy as np
 import scipy.sparse
 from scipy.stats import entropy
-import scipy.linalg
+from scipy.linalg import get_blas_funcs, triu
 from scipy.linalg.lapack import get_lapack_funcs
-from scipy.linalg.special_matrices import triu
 from scipy.special import psi  # gamma function utils
 
 
@@ -42,7 +41,7 @@ def blas(name, ndarray):
         BLAS function for the needed operation on the given data type.
 
     """
-    return scipy.linalg.get_blas_funcs((name,), (ndarray,))[0]
+    return get_blas_funcs((name,), (ndarray,))[0]
 
 
 def argsort(x, topn=None, reverse=False):