title: No module named 'sklearn.externals.joblib' ERROR
body: <p>i am trying to implement a bayesian optimization but already starting having an error while importing 'gp_minimize' from scikit-optimize package
  from skopt import gp_minimize</p>
  <p>`</p>
  <pre><code>res = gp_minimize(f,                  # the function to minimize
                    [(-2.0, 2.0)],      # the bounds on each dimension of x
                    acq_func=&quot;EI&quot;,      # the acquisition function
                    n_calls=15,         # the number of evaluations of f
                    n_random_starts=5,  # the number of random initialization points
                    noise=0.1**2,       # the noise level (optional)
                    random_state=1234)   # the random seed*
  ---------------------------------------------------------------------------
  ModuleNotFoundError                       Traceback (most recent call last)
  &lt;ipython-input-13-8761d45476ed&gt; in &lt;module&gt;
  ----&gt; 1 from skopt import gp_minimize
        2 
        3 res = gp_minimize(f,                  # the function to minimize
        4                   [(-2.0, 2.0)],      # the bounds on each dimension of x
        5                   acq_func=&quot;EI&quot;,      # the acquisition function
  
  ~\Anaconda3\lib\site-packages\skopt\__init__.py in &lt;module&gt;
       50 from . import benchmarks
       51 from . import callbacks
  ---&gt; 52 from . import learning
       53 from . import optimizer
       54 
  
  ~\Anaconda3\lib\site-packages\skopt\learning\__init__.py in &lt;module&gt;
        4 from .forest import ExtraTreesRegressor
        5 from .gaussian_process import GaussianProcessRegressor
  ----&gt; 6 from .gbrt import GradientBoostingQuantileRegressor
        7 
        8 
  
  ~\Anaconda3\lib\site-packages\skopt\learning\gbrt.py in &lt;module&gt;
        5 from sklearn.ensemble import GradientBoostingRegressor
        6 from sklearn.utils import check_random_state
  ----&gt; 7 from sklearn.externals.joblib import Parallel, delayed
        8 
        9 
  
  ModuleNotFoundError: No module named 'sklearn.externals.joblib'
  </code></pre>
  <p>`
  I already downloaded all required packages such joblib and scikit learn and scikit optimize, so can't figure out why it's not working.</p>