bump test python version to 3.7-3.9 (#244)

* bump test python version to 3.7-3.10

* rm 3.10

* fix test error

Author: njzjz

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8, 3.9]
 
     steps:
     - uses: actions/checkout@v2

dpdata/vasp/outcar.py

@@ -20,7 +20,7 @@ def system_info (lines, type_idx_zero = False) :
             m = re.search(r'NELM\s*=\s*(\d+)', ii)
             if m:
                 nelm = int(m.group(1))
-        elif 'ions per type' in ii :
+        if 'ions per type' in ii :
             atom_numbs_ = [int(s) for s in ii.split()[4:]]
             if atom_numbs is None :                
                 atom_numbs = atom_numbs_