Fix wrong Ruby SHA and replace with sha256sum

[ci skip]

doc/install/installation.md

@@ -124,7 +124,7 @@ Download Ruby and compile it:
 
     mkdir /tmp/ruby && cd /tmp/ruby
     curl -O --progress https://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.4.tar.gz
-    echo 'e2e195a4a58133e3ad33b955c829bb536fa3c075  ruby-2.2.4.tar.gz' | shasum -c - && tar xzf ruby-2.2.4.tar.gz
+    echo 'b6eff568b48e0fda76e5a36333175df049b204e91217aa32a65153cc0cdcb761  ruby-2.2.4.tar.gz' | sha256sum -c - && tar xzf ruby-2.2.4.tar.gz
     cd ruby-2.2.4
     ./configure --disable-install-rdoc
     make