fix(gatsby-remark-copy-linked-files): respect assetPrefix (gatsbyjs#2…

…6976)

* test(gatsby-remarkc-copy-linked-files): get rid of "undefined" in assertions - it doesn't inspire confidence

* fix(gatsby-remark-copy-linked-files): honor assetPrefix correctly

Co-authored-by: gatsbybot <mathews.kyle+gatsbybot@gmail.com>

yarn.lock

@@ -1922,12 +1922,7 @@
     "@types/node" "*"
     form-data "^3.0.0"
 
-"@types/node@*":
-  version "14.10.2"
-  resolved "https://registry.yarnpkg.com/@types/node/-/node-14.10.2.tgz#9b47a2c8e4dabd4db73b57e750b24af689600514"
-  integrity sha512-IzMhbDYCpv26pC2wboJ4MMOa9GKtjplXfcAqrMeNJpUUwpM/2ATt2w1JPUXwS6spu856TvKZL2AOmeU2rAxskw==
-
-"@types/node@^8.5.7":
+"@types/node@*", "@types/node@^8.5.7":
   version "8.10.63"
   resolved "https://registry.yarnpkg.com/@types/node/-/node-8.10.63.tgz#f86775d576bc07a2992da244f41c23d3ba66d402"
   integrity sha512-g+nSkeHFDd2WOQChfmy9SAXLywT47WZBrGS/NC5ym5PJ8c8RC6l4pbGaUW/X0+eZJnXw6/AVNEouXWhV4iz72Q==