Remove github links from 'metadig-worker' in 'requirements.txt' file …

…for requests, pandas and python-magic, libraries can be found in pypi

Docker/metadig-worker/requirements.txt

@@ -1,6 +1,6 @@
 numpy
 metadig @ git+https://github.com/NCEAS/metadig-py.git@feature-store-interface
 hashstore @ git+https://github.com/DataONEorg/hashstore.git
-requests @ git+https://github.com/psf/requests.git
-pandas @ git+https://github.com/pandas-dev/pandas.git
-python-magic @ git+https://github.com/ahupp/python-magic.git
+requests
+pandas
+python-magic