fix travis ci tf versions

Author: cjekel

.travis.yml

@@ -10,7 +10,7 @@ install:
   - pip install . --no-cache-dir
 script:
   - pytest --cov=pwlf -p no:warnings tests/tests.py
-  - pip install tensorflow<=2.0.0
+  - pip install "tensorflow>=1.0.0,<2.0.0"
   - pytest --cov=pwlf --cov-append -p no:warnings tests/teststf.py
 before_script:
   - flake8 pwlf

setup.py

@@ -7,25 +7,28 @@
     exec(fp.read(), version)
 
 setup(
-    name='pwlf',
+    name="pwlf",
     version=version["__version__"],
-    author='Charles Jekel',
-    author_email='cjekel@gmail.com',
-    packages=['pwlf'],
-    url='https://github.com/cjekel/piecewise_linear_fit_py',
-    license='MIT License',
-    description='fit piecewise linear functions to data',
-    long_description=io.open('README.rst', encoding="utf-8").read(),
+    author="Charles Jekel",
+    author_email="cjekel@gmail.com",
+    packages=["pwlf"],
+    url="https://github.com/cjekel/piecewise_linear_fit_py",
+    license="MIT License",
+    description="fit piecewise linear functions to data",
+    long_description=io.open("README.rst", encoding="utf-8").read(),
     # long_description_content_type='text/markdown',
-    platforms=['any'],
+    platforms=["any"],
     install_requires=[
         "numpy >= 1.14.0",
         "scipy >= 1.2.0",
         "pyDOE >= 0.3.8",
     ],
     classifiers=[
-        'License :: OSI Approved :: MIT License',
-        'Programming Language :: Python :: 3',
+        "License :: OSI Approved :: MIT License",
+        "Programming Language :: Python :: 3",
     ],
     python_requires=">3.5",
+    extras_require={
+        "PiecewiseLinFitTF": ["tensorflow < 2.0.0"],
+    },
 )