fix(jinja): use json filter

[noelmcloughlin]

PR progress checklist (to be filled in by reviewers)

• Changes to documentation are appropriate (or tick if not required)
• Changes to tests are appropriate (or tick if not required)
• Reviews completed

---

What type of PR is this?

Primary type

• [build] Changes related to the build system
• [chore] Changes to the build process or auxiliary tools and libraries such as documentation generation
• [ci] Changes to the continuous integration configuration
• [feat] A new feature
• [fix] A bug fix
• [perf] A code change that improves performance
• [refactor] A code change that neither fixes a bug nor adds a feature
• [revert] A change used to revert a previous commit
• [style] Changes that do not affect the meaning of the code (white-space, formatting, missing semi-colons, etc.)

Secondary type

• [docs] Documentation changes
• [test] Adding missing or correcting existing tests

Does this PR introduce a BREAKING CHANGE?

No.

Related issues and/or pull requests

Describe the changes you're proposing

Bug fix:

Running scope as unit run-5386.scope.
                    No package u'libicu' available.
                    Error: Nothing to do

But package is there:

# yum install libicu
Resolving Dependencies
--> Running transaction check
---> Package libicu.x86_64 0:50.2-3.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
=======================================================================================================================================
 Package                        Arch                           Version                              Repository                    Size
=======================================================================================================================================
Installing:
 libicu                         x86_64                         50.2-3.el7                           base                         6.9 M
Transaction Summary
=======================================================================================================================================
Install  1 Package
Total download size: 6.9 M
Installed size: 24 M
Is this ok [y/d/N]: n

Pillar / config required to test the proposed changes

Debug log showing how the proposed changes work

Documentation checklist

• Updated the README (e.g. Available states).
• Updated pillar.example.

Testing checklist

• Included in Kitchen (i.e. under state_top).
• Covered by new/existing tests (e.g. InSpec, Serverspec, etc.).
• Updated the relevant test pillar.

Additional context

[vutny]

Good stuff

[saltstack-formulas-travis]

🎉 This PR is included in version 0.41.8 🎉

The release is available on GitHub release

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