NEP29: Set minimum required version to NumPy 1.21+ (#2389)

Following NEP29 policy. Bumps minimum supported
NumPy version to 1.21 in the pyproject.toml, requirements.txt
and environment.yml files. Also update installation documentation
to mention NumPy 1.21+ requirement.

README.rst

@@ -261,7 +261,7 @@ Compatibility with GMT/Python/NumPy versions
       - `Dev Documentation <https://www.pygmt.org/dev>`_ (reflects `main branch <https://github.com/GenericMappingTools/pygmt>`_)
       - >=6.3.0
       - >=3.8
-      - >=1.20
+      - >=1.21
     * - `v0.8.0 <https://github.com/GenericMappingTools/pygmt/releases/tag/v0.8.0>`_ (latest release)
       - `v0.8.0 Documentation <https://www.pygmt.org/v0.8.0>`_
       - >=6.3.0

ci/requirements/docs.yml

@@ -6,7 +6,7 @@ dependencies:
     # Required dependencies
     - pip
     - gmt=6.4.0
-    - numpy>=1.20
+    - numpy>=1.21
     - pandas
     - xarray
     - netCDF4

doc/install.rst

@@ -97,7 +97,7 @@ Dependencies
 
 PyGMT requires the following libraries to be installed:
 
-* `numpy <https://numpy.org>`__ (>= 1.20)
+* `numpy <https://numpy.org>`__ (>= 1.21)
 * `pandas <https://pandas.pydata.org>`__
 * `xarray <https://xarray.dev/>`__
 * `netCDF4 <https://unidata.github.io/netcdf4-python>`__

environment.yml

@@ -6,7 +6,7 @@ dependencies:
     # Required dependencies
     - pip
     - gmt=6.4.0
-    - numpy>=1.20
+    - numpy>=1.21
     - pandas
     - xarray
     - netCDF4

pyproject.toml

@@ -32,7 +32,7 @@ classifiers = [
     "License :: OSI Approved :: BSD License",
 ]
 dependencies = [
-    "numpy>=1.20",
+    "numpy>=1.21",
     "pandas",
     "xarray",
     "netCDF4",

requirements.txt

@@ -1,5 +1,5 @@
 # Required packages
-numpy>=1.20
+numpy>=1.21
 pandas
 xarray
 netCDF4