[PATCH] Fix Army camp decay rate warning

[Stan]

Since r17061 Atlas gives a warning when loading the army camp, it is because it doesn't support 37.5 and expect 38 or 37 instead

<p class="error">ERROR: RelaxNGValidator: Validation error: structures/rome_army_camp:1: Type positiveInteger doesn't allow value '37.5'</p>
<p class="error">ERROR: RelaxNGValidator: Validation error: structures/rome_army_camp:1: Error validating datatype positiveInteger</p>
<p class="error">ERROR: RelaxNGValidator: Validation error: structures/rome_army_camp:1: Element DecayRate failed to validate content</p>
<p class="error">ERROR: RelaxNGValidator: Validation failed for '(null)'</p>
<p class="error">ERROR: Failed to validate entity template 'structures/rome_army_camp'</p>

[Stan]

Proposed Fix

[Itms]

In 17072:

Make the territory decay rate a decimal value. Fixes #3449.