#955 Fix CI build

Freezing numpy and scipy was a bad idea.
I freeze matplotlib  dependend  on the python version only.

appveyor.yml

@@ -7,14 +7,19 @@ environment:
   matrix:
     - PYTHON_VERSION: 3.5
       MINICONDA: C:\Miniconda35-x64
+      MPL_VERSION: 3.0.0
     - PYTHON_VERSION: 3.6
       MINICONDA: C:\Miniconda3-x64
+      MPL_VERSION: 3.3.4
     - PYTHON_VERSION: 3.7
       MINICONDA: C:\Miniconda3-x64
+      MPL_VERSION: 3.3.4
     - PYTHON_VERSION: 3.8
       MINICONDA: C:\Miniconda3-x64
+      MPL_VERSION: 3.3.4
     - PYTHON_VERSION: 3.9
       MINICONDA: C:\Miniconda3-x64
+      MPL_VERSION: 3.3.4
 
 #configuration:
 #  - Debug
@@ -25,8 +30,8 @@ install:
  - conda config --set always_yes yes --set changeps1 no
  - conda update -q conda
  - conda info -a
-# github issue #955: freez build versions of numpy, scipy and matplotlib
- - "conda create -q -n build-environment python=%PYTHON_VERSION% numpy=1.19.2 scipy=1.5.2 matplotlib=3.3.4"
+# github issue #955: freeze build version of matplotlib
+ - "conda create -q -n build-environment python=%PYTHON_VERSION% numpy scipy matplotlib=%MPL_VERSION%"
  - activate build-environment
  # We need wheel installed to build wheels
  - python -m pip install wheel

setup.py

@@ -117,13 +117,13 @@ try:
 except ModuleNotFoundError:
     ext_mods = []
 
-# #955
-install_requirements = ['numpy==1.19.2', 'six', 'paramz>=0.9.0', 'cython>=0.29']
+install_requirements = ['numpy>=1.7', 'six', 'paramz>=0.9.0', 'cython>=0.29']
+matplotlib_version = 'matplotlib==3.3.4'
 if sys.version_info < (3, 6):
     install_requirements += ['scipy>=1.3.0,<1.5.0']
+    matplotlib_version = 'matplotlib==3.0.0'
 else:
-    # #955
-    install_requirements += ['scipy==1.5.2']
+    install_requirements += ['scipy>=1.3.0']
 
 setup(name = 'GPy',
       version = __version__,
@@ -170,15 +170,14 @@ setup(name = 'GPy',
       include_package_data = True,
       py_modules = ['GPy.__init__'],
       test_suite = 'GPy.testing',
-      # #955
-      setup_requires = ['numpy == 1.19.2'],
+      setup_requires = ['numpy>=1.7'],
       install_requires = install_requirements,
       extras_require = {'docs':['sphinx'],
                         'optional':['mpi4py',
                                     'ipython>=4.0.0',
                                     ],
                         #matplotlib Version see github issue #955
-                        'plotting':['matplotlib == 3.3.4',
+                        'plotting':[matplotlib_version,
                                     'plotly >= 1.8.6'],
                         'notebook':['jupyter_client >= 4.0.6',
                                     'ipywidgets >= 4.0.3',