add subclass to prevent spawn errors when using server side

lib/codabar.js

@@ -2,7 +2,7 @@
  * barcode generator - codabar
  */
 
-var gm = require('gm');
+var gm = require('gm').subClass({ imageMagick: true });
 
 var bmap = {
 	'0': [0,0,0,0,0,1,1],

lib/code128.js

@@ -2,7 +2,7 @@
  * barcode generator - code128
  */
 
-var gm = require('gm');
+var gm = require('gm').subClass({ imageMagick: true });
 
 const BARMAP = [
   [2,1,2,2,2,2], [2,2,2,1,2,2], [2,2,2,2,2,1], [1,2,1,2,2,3], [1,2,1,3,2,2],

lib/code39.js

@@ -2,7 +2,7 @@
  * barcode generator - code39
  */
 
-var gm = require('gm');
+var gm = require('gm').subClass({ imageMagick: true });
 
 const bmap = {
 	' ': [0,1,1,0,0,0,1,0,0],

lib/ean13.js

@@ -2,7 +2,7 @@
  * barcode generator - EAN13 (ISBN)
  */
 
-var gm = require('gm'),
+var gm = require('gm').subClass({ imageMagick: true }),
   getCheckDigit = require('./utils/checksums').weight3even10,
   Barcode1D = require('./utils/draw1D');
 

lib/upc-a.js

@@ -2,7 +2,7 @@
  * barcode generator - UPC-A
  */
 
-var gm = require('gm'),
+var gm = require('gm').subClass({ imageMagick: true }),
   getCheckDigit = require('./utils/checksums').weight3odd10,
   Barcode1D = require('./utils/draw1D');
 

lib/utils/draw1D.js

@@ -6,7 +6,7 @@
  * not rely on it, rather please use the Barcode2D drawer instead.
  */
 
-var gm = require('gm');
+var gm = require('gm').subClass({ imageMagick: true });
 
 const MODE_BINARY = 0;
 const MODE_BARWIDTH = 1;

lib/utils/draw2D.js

@@ -28,7 +28,7 @@
  * your baseheight.
  */
 
-var gm = require('gm');
+var gm = require('gm').subClass({ imageMagick: true });
 
 /*
  * Basic constructor