Updating dependencies to avoid conflicts

sempy_core/requirements.txt

-numpy>=1.20.2
-spiceypy>=4.0.0
-scipy>=1.6.2
-matplotlib>=3.4.1
-cffi>=1.14.4
-multiprocess>=0.70.11.1
-numba>=0.53.1
-orekit>=10.3
-psutil>=5.8.0
-pykep>=2.6
-tqdm>=4.59.0
-pygmo>=2.16.1
-python>=3.8.5
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+numpy==1.20.2
+spiceypy==4.0.0
+scipy==1.6.2
+matplotlib==3.4.1
+cffi==1.14.4
+multiprocess==0.70.11.1
+numba==0.53.1
+orekit==10.3
+psutil==5.8.0
+pykep==2.6
+tqdm==4.59.0
+pygmo==2.16.1
+python==3.8.5
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