remove vignettes for now as wont build on r-devel

Author: sckott

DESCRIPTION

@@ -14,7 +14,6 @@ Authors@R: person("Scott", "Chamberlain", role = c("aut", "cre"),
     email = "[email protected]")
 URL: https://github.com/ropensci/elastic
 BugReports: https://github.com/ropensci/elastic/issues
-VignetteBuilder: knitr
 Imports:
     utils,
     methods,
@@ -23,6 +22,5 @@ Imports:
     jsonlite (>= 1.1)
 Suggests:
     roxygen2 (>= 6.0.1),
-    testthat,
-    knitr
+    testthat
 RoxygenNote: 6.0.1