make invariants check follow the same pattern as other insertions

.../main/java/org/atlanmod/commons/assertions/Assertion.java

...ava/org/atlanmod/commons/assertions/BooleanAssertion.java

...n/java/org/atlanmod/commons/assertions/DateAssertion.java

...java/org/atlanmod/commons/assertions/DoubleAssertion.java

.../java/org/atlanmod/commons/assertions/FloatAssertion.java

...in/java/org/atlanmod/commons/assertions/IntAssertion.java

...n/java/org/atlanmod/commons/assertions/LongAssertion.java

...java/org/atlanmod/commons/assertions/ObjectAssertion.java

...test/java/org/atlanmod/commons/assertions/AssertTest.java

...g/atlanmod/commons/assertions/InvariantAssertionTest.java