chore: change repository protocol from deprecated git to https (#230)

https://github.blog/security/application-security/improving-git-protocol-security-github/

Co-authored-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>

Author: e-kwsm

README.markdown

@@ -22,7 +22,7 @@ Please report bugs via the
 
 Master [git mirror](https://github.com/haskell/statistics):
 
-* `git clone git://github.com/haskell/statistics.git`
+* `git clone https://github.com/haskell/statistics.git`
 
 # Authors