fix installation error for Python3.8+

.travis.yml

@@ -4,6 +4,7 @@ python:
     - "3.5"
     - "3.6"
     - "3.7"
+    - "3.8"
 install:
     - python setup.py install
     - pip install coveralls

setup.py

@@ -67,6 +67,15 @@ def extensions():
     return cythonize(extensions)
 
 
+def switch_install_requires():
+    major = sys.version_info.major
+    minor = sys.version_info.minor
+    if os.name == 'posix' and major == 3 and minor > 7:
+        return ['six', 'numpy', 'DyNet38']
+    else:
+        return ['six', 'numpy', 'DyNet']
+
+
 setup(
     name='nagisa',
     packages=['nagisa'],
@@ -81,7 +90,7 @@ def extensions():
     license='MIT License',
     platforms='Unix',
     setup_requires=['six', 'cython', 'numpy'],
-    install_requires=['six', 'numpy', 'DyNet'],
+    install_requires=switch_install_requires(),
     classifiers=classifiers,
     include_package_data=True,
     test_suite='test.nagisa_test.suite',