Update version of clang format in CODING_STANDARDs

Was saying 3.8, but CBMC moved to version 7 in #3245

Author: Thomas Kiley

CODING_STANDARD.md

@@ -315,13 +315,13 @@ To avoid waiting until you've made a PR to find formatting issues, you can
 install clang-format locally and run it against your code as you are working.
 
 Different versions of clang-format have slightly different behaviors. CBMC uses
-clang-format-3.8 as it is available the repositories for Ubuntu 16.04 and
+clang-format-7.0 as it is available the repositories for Ubuntu 18.04 and
 Homebrew.
 To install on a Unix-like system, try installing using the system package
 manager:
 ```
-apt-get install clang-format-3.8  # Run this on Ubuntu, Debian etc.
-brew install clang-format@3.8     # Run this on a Mac with Homebrew installed
+apt-get install clang-format-8  # Run this on Ubuntu, Debian etc.
+brew install clang-format@8     # Run this on a Mac with Homebrew installed
 ```
 
 If your platform doesn't have a package for clang-format, you can download a
@@ -333,18 +333,21 @@ the [LLVM Snapshot Builds page](http://llvm.org/builds/).
 
 ### FORMATTING A RANGE OF COMMITS
 
-Clang-format is distributed with a driver script called git-clang-format-3.8.
+Clang-format is distributed with a driver script called git-clang-format-7.
 This script can be used to format git diffs (rather than entire files).
 
 After committing some code, it is recommended to run:
 ```
-git-clang-format-3.8 upstream/develop
+git-clang-format-7 upstream/develop
 ```
 *Important:* If your branch is based on a branch other than `upstream/develop`,
 use the name or checksum of that branch instead. It is strongly recommended to
 rebase your work onto the tip of the branch it's based on before running
 `git-clang-format` in this way.
 
+Note: git-clang-format uses the git config variable `clangformat.binary` so if you 
+have multiple versions of clang-format installed, you might need to update this.
+
 ### RETROACTIVELY FORMATTING INDIVIDUAL COMMITS
 
 If your works spans several commits and you'd like to keep the formatting
@@ -355,7 +358,7 @@ The following command will stop at each commit in the range and run
 clang-format on the diff at that point.  This rewrites git history, so it's
 *unsafe*, and you should back up your branch before running this command:
 ```
-git filter-branch --tree-filter 'git-clang-format-3.8 upstream/develop' \
+git filter-branch --tree-filter 'git-clang-format-7 upstream/develop' \
   -- upstream/develop..HEAD
 ```
 *Important*: `upstream/develop` should be changed in *both* places in the