fix(styles): inline all styles on optimization phase

By definition, a defs sprite is not usable as a CSS sprite
fix #19

lib/svg.js

@@ -4,6 +4,7 @@ import cleanupIDs from 'svgo/plugins/cleanupIDs'
 import removeAttrs from 'svgo/plugins/removeAttrs'
 import removeDimensions from 'svgo/plugins/removeDimensions'
 import removeViewBox from 'svgo/plugins/removeViewBox'
+import inlineStyles from 'svgo/plugins/inlineStyles'
 
 // Enable removeAttrs plugin
 // Remove id attribute to prevent conflict with our id
@@ -15,12 +16,18 @@ removeAttrs.params.attrs = 'svg:id'
 removeViewBox.active = false
 removeDimensions.active = true
 
+// Make all styles inline
+// By definition, a defs sprite is not usable as a CSS sprite
+inlineStyles.active = true
+inlineStyles.params.onlyMatchedOnce = false
+
 const svgOptimizer = new Svgo({
   pluging: [
     removeDimensions,
     cleanupIDs,
     removeAttrs,
-    removeViewBox
+    removeViewBox,
+    inlineStyles
   ]
 })