py-mpmath: updated to 1.2.1

--1.2.0--
Released February 1, 2021

Features and optimizations:

* Support @ operator for matrix multiplication (Max Gaukler)
* Add eta() implementing the Dedekind eta function
* Optimized the python_trailing function (adhoc-king)
* Implement unary plus for matrices (Max Gaukler)
* Improved calculation of gram_index (p15-git-acc)

Compatibility:

* Enable sage backend by default only if SAGE_ROOT is set (Pauli Virtanen)
* Fix syntax warnings on CPython 3.8 (Sergey B Kirpichev)
* Changed version requirements to Python 2.7 and 3.4 or later
  (Sergey B Kirpichev)
* Improvements to the setup and test code (Sergey B Kirpichev)
* Fix sys.version comparisons for compatibility with Python 3.10 (Jakub Wilk)
* Fixes to Python2/3 compatibility for printing (Christian Clauss)

Bug fixes:

* Fix a possible division by zero in shanks() (Pascal Hebbeker)
* Fixed indexing errors in deHoog, Knight & Stokes inverse laplace
  transform algorithm (Kris Kuhlman)
* Corrected branch cuts of the elliprj() function in some cases
* Fix initialization of iv.matrix from non-interval matrix (Max Gaukler)
* Preserve function signatures in PrecisionManager (Viet Tran)
* Implemented float and complex conversions for ivmpf
  (Jonathan Warner)
* Fixed issue with scalar-matrix multiplication for interval matrices
  (Jonathan Warner)
* Fix estimation of quadrature error with multiple subintervals (Tom Minka)
* Fixed a problem with the defun decorators (Sergey B Kirpichev)
* Fix eigenvalue sorting by absolute value (Georg Ostrovski)

Cleanup:

* Documentation corrections (Paul Masson, S.Y. Lee)
* Remove inaccessible logic in fsum/fdot (Sergey B Kirpichev)
* Remove broken force_type option for matrix constructor (Max Gaukler)
* Fix text of the BSD license in LICENSE (Sergey B Kirpichev)
* Minor code cleanup (Fr辿d辿ric Chapoton)
* Removed old, unused code

(adam)