Update to python 3.9 and nlopt 2.7.0

Author: DanielBok

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       fail-fast: False
       matrix:
-        python-version: [ 3.6, 3.7, 3.8 ]
+        python-version: [ 3.6, 3.7, 3.8, 3.9 ]
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2
@@ -101,7 +101,7 @@ jobs:
     strategy:
       matrix:
         os: [ windows-latest, ubuntu-latest, macos-latest ]
-        python-version: [ 3.6, 3.7, 3.8 ]
+        python-version: [ 3.6, 3.7, 3.8, 3.9 ]
 
     steps:
       - name: Checkout repository

extern/nlopt

@@ -13,13 +13,10 @@ description = Library for nonlinear optimization, wrapping many algorithms for g
 long_description = file: README.md
 long_description_content_type = text/markdown
 keywords =
-    copula
-    copulae
-    dependency modelling
-    dependence structures
-    archimdean
-    elliptical
-    finance
+    algorithms
+    global local constrained unconstrained optimization
+    optimization
+    non-linear optimization
 classifiers =
     Development Status :: 5 - Production
     Intended Audience :: End Users/Desktop
@@ -32,6 +29,7 @@ classifiers =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
     Topic :: Scientific/Engineering
 
 [options]