title: Get the First day and the last day of month from an Instant
body: <p>I have a method using 2 Instants in parameters <code>getIssuesBillable(Instant start, Instant end, ....)</code>, my question is how I get the first day of a month and the last day of the month using a Java 8 Instant? 
  I already tried use <strong><code>withDayOfMonth()</code></strong>, and <strong><code>lengthOfMonth()</code></strong>:</p>
  
  <pre><code>LocalDate initial = LocalDate.now();
  LocalDate start = initial.withDayOfMonth(firstDayOfMonth());
  LocalDate end = initial.withDayOfMonth(lastDayOfMonth());
  </code></pre>
  
  <p>But in this case, I need to convert and make some workarounds in this case, if someone knows a better way to do it I really appreciate any response.</p>