Fix typo: pont() --> point()

[flake8](http://flake8.pycqa.org) testing of https://github.com/USTC-Resource/USTC-Course on Python 3.7.1

$ __flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics__
```
./算法基础/labs/2018-徐云/lab1/PB16030899-朱河勤-实验一.py:11:16: F821 undefined name 'pont'
        return pont(-self.x, -self.y)
               ^
./数理逻辑/codes/mbinary/system_L.py:220:23: E999 TabError: inconsistent use of tabs and spaces in indentation
	s=s.replace('<->','-')
                      ^
./数据结构/codes/mbinary/graph/directed.py:49:9: F821 undefined name 'self'
        self.vertexs[i]= x
        ^
./数据结构/codes/mbinary/graph/directed.py:49:22: F821 undefined name 'i'
        self.vertexs[i]= x
                     ^
./数据结构/codes/mbinary/graph/adjacentList.py:55:9: F821 undefined name 'self'
        self.vertexs[i]= x
        ^
./数据结构/codes/mbinary/graph/adjacentList.py:104:33: F821 undefined name 'e'
            while arc.nextEdge!=e:
                                ^
./数据结构/codes/mbinary/graph/adjacentList.py:112:41: F821 undefined name 'e'
                    while arc.nextEdge!=e:
                                        ^
./数据结构/codes/mbinary/graph/undirected.py:60:9: F821 undefined name 'self'
        self.vertexs[i]= x
        ^
./数据结构/labs/2017/navigation/graph.py:52:9: F821 undefined name 'self'
        self.vertexs[i]= x
        ^
./数据结构/labs/2017/navigation/directed.py:39:9: F821 undefined name 'self'
        self.vertexs[i]= x
        ^
./数据结构/labs/2017/navigation/directed.py:39:22: F821 undefined name 'i'
        self.vertexs[i]= x
                     ^
1     E999 TabError: inconsistent use of tabs and spaces in indentation
10    F821 undefined name 'self'
11
```
__E901,E999,F821,F822,F823__ are the "_showstopper_" [flake8](http://flake8.pycqa.org) issues that can halt the runtime with a SyntaxError, NameError, etc. These 5 are different from most other flake8 issues which are merely "style violations" -- useful for readability but they do not effect runtime safety.
* F821: undefined name `name`
* F822: undefined name `name` in `__all__`
* F823: local variable name referenced before assignment
* E901: SyntaxError or IndentationError
* E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree

Author: cclauss

算法基础/labs/2018-徐云/lab1/PB16030899-朱河勤-实验一.py

@@ -8,7 +8,7 @@ def __init__(self,x,y):
         self.x=x
         self.y=y
     def __neg__(self):
-        return pont(-self.x, -self.y)
+        return point(-self.x, -self.y)
     def __len__(self):
         return self.norm(2)
     def __lt__(self,p):