text: Title: `word2vec.doesnt_match` numpy vstack deprecation warning 
  Body: #### Problem description
  
  I followed [this instruction](https://radimrehurek.com/gensim/scripts/glove2word2vec.html) to load GloVe model. When I run:  `model.doesnt_match("breakfast cereal dinner lunch".split())` from the [tutorial](https://rare-technologies.com/word2vec-tutorial/), it produces FutureWarning on the `vstack` function. It seems that [I am not the first person to encounter this error as well](https://stackoverflow.com/questions/56593904/word2vec-doesnt-match-function-throws-numpy-warning). It might also be similar to [Issue 2432](https://github.com/RaRe-Technologies/gensim/issues/2432). The error reads:  
  
  > C:\Path_to_gensim\keyedvectors.py:877:  FutureWarning: arrays to stack must be passed as a "sequence" type such as list or tuple. Support for non-sequence iterables such as generators is deprecated as of NumPy 1.16 and will raise an error in the future.  
  > vectors = vstack(self.word_vec(word, use_norm=True) for word in used_words).astype(REAL)   
  
  #### Steps/code/corpus to reproduce
  
  ```python  
  from gensim.test.utils import datapath, get_tmpfile  
  from gensim.models import KeyedVectors  
  from gensim.scripts.glove2word2vec import glove2word2vec  
  
  glove_file = datapath('test_glove.txt')  
  tmp_file = get_tmpfile("test_word2vec.txt")  
  _ = glove2word2vec(glove_file, tmp_file)  
  model = KeyedVectors.load_word2vec_format(tmp_file)  
  model.doesnt_match("breakfast cereal dinner lunch".split())
  
  ```
  
  #### Versions
  
  ```python
  Windows-10-10.0.17763-SP0   
  python 3.8.2   (tags/v3.8.2:7b3ab59, Feb 25 2020, 23:03:10) [MSC v.1916 64 bit (AMD64)]   
  Bits 64   
  NumPy 1.19.0   
  SciPy 1.5.2   
  gensim 3.8.3   
  FAST_VERSION 0
  ```