Fix warning "Renderer command uses a path relative to the renderer output directory ..." (rust-lang#1194)

Author: steffahn

src/doc/rustc-dev-guide/book.toml

@@ -19,7 +19,7 @@ enable = true
 level = 0
 
 [output.linkcheck]
-command = "../../ci/linkcheck.sh"
+command = "ci/linkcheck.sh"
 follow-web-links = true
 exclude = [ "crates\\.io", "gcc\\.godbolt\\.org", "youtube\\.com", "youtu\\.be", "dl\\.acm\\.org", "cs\\.bgu\\.ac\\.il", "www\\.amazon\\.com", "www\\.rustaceans\\.org", "play\\.rust-lang\\.org" ]
 cache-timeout = 86400