Fix the speeling of "purgeable" in Gr code

TBR=robertphillips@google.com

Review URL: https://codereview.chromium.org/874693002
diff --git a/src/gpu/GrGpuResourceCacheAccess.h b/src/gpu/GrGpuResourceCacheAccess.h
index 474438f..aa2337d 100644
--- a/src/gpu/GrGpuResourceCacheAccess.h
+++ b/src/gpu/GrGpuResourceCacheAccess.h
@@ -86,7 +86,7 @@
      */
     void release() {
         fResource->release();
-        if (fResource->isPurgable()) {            
+        if (fResource->isPurgeable()) {            
             SkDELETE(fResource);
         }
     }
@@ -96,7 +96,7 @@
      */
     void abandon() {
         fResource->abandon();
-        if (fResource->isPurgable()) {            
+        if (fResource->isPurgeable()) {            
             SkDELETE(fResource);
         }
     }