Fix a few typos and improve syntax highlighting

CentOS6.md

@@ -1,12 +1,15 @@
 _Note: Haskell Platform v7.10.3 and v8.0.1 requires glibc v2.14 but CentOS 6 has v2.12 so be sure to download v7.10.2-a release from their [prior releases](https://www.haskell.org/platform/prior.html) page._
 
 # Deps
+```sh
 yum groupinstall "Development Tools" -y
 yum install gmp-devel # may need epel
 sudo ln -s /usr/lib64/libgmp.so.3  /usr/lib64/libgmp.so.10
+```
 
 # Get Haskell and build it
 #### Based on https://www.haskell.org/platform/linux.html#linux-generic 
+```sh
 dir="$(mktemp -d)"
 pushd "$dir"
 wget https://haskell.org/platform/download/7.10.2/haskell-platform-7.10.2-a-unknown-linux-deb7.tar.gz
@@ -14,10 +17,15 @@ _Note: Haskell Platform v7.10.3 and v8.0.1 requires glibc v2.14 but CentOS 6 has
 ./install-haskell-platform.sh
 popd
 rm -r "$dir"
-# Install shellcheck
+```
+
+# Install ShellCheck
+```sh
 cabal update
 cabal install shellcheck
+```
 
 # Place it in a global directory
+```sh
 cp ~/.cabal/bin/shellcheck /usr/local/bin # portable to other el6 systems without Haskell
-
+```