title: latitude error when converting ESPG:3857 to ESPG:4326 with proj4js
body: <p>After rewriting my Ruby coordinate conversion code to Node.js with Proj4js I'm always getting the same error of 0.17876359947293707 in latitude:</p>
  
  <pre><code>var proj4 = require('proj4js');
  function(pair) {
     var firstProjection = "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +units=m +k=1.0 +nadgrids=@null +no_defs"
     var secondProjection = "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"
     return proj4(firstProjection, secondProjection, pair);
   }([4156404,7480076.5]) 
  
  [ 37.33761240175516, 55.7832340897427 ]
  </code></pre>
  
  <p>Ruby code gives me [37.33761240175515, 55.60447049026976] which is same as <a href="http://cs2cs.mygeodata.eu/" rel="nofollow">http://cs2cs.mygeodata.eu/</a> with projection strings from above.</p>
  
  <p>Any ideas would be appreciated, thank you!</p>