Fix 2534 ie11 load problem (RELEASE 2017.06.00)

[MV88]

Description

We used a method not supported for IE11

Issues

• Fix Cannot load map on IE11 #2534

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
#2534

What is the new behavior?
maps loads correctly, and toc filters layes name correctly

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:

[coveralls]

Coverage increased (+0.001%) to 80.981% when pulling 0e07a08 on MV88:2534_ie11_load_problem into 1198580 on geosolutions-it:2017.06.00.