Fixed doc-coverage, skip build on 6.3 due to lack of scribble/example

.travis.yml

@@ -8,7 +8,7 @@ env:
     - PATH="$RACKET_DIR/bin:$PATH"
   matrix:
     # RACKET_VERSION is an argument to install-racket.sh
-    - RACKET_VERSION=6.3
+    #- RACKET_VERSION=6.3 # scribble/example is available on ≥ 6.4
     - RACKET_VERSION=6.4
     - RACKET_VERSION=6.5
     - RACKET_VERSION=6.6
@@ -28,7 +28,7 @@ install:
 script:
 - raco test -x -p "$(basename "$TRAVIS_BUILD_DIR")"
 - raco setup --check-pkg-deps --unused-pkg-deps --no-zo --no-launcher --no-install --no-post-install --no-docs --pkgs "$(basename "$TRAVIS_BUILD_DIR")"
-- raco doc-coverage "$(basename "$TRAVIS_BUILD_DIR")"
+- raco doc-coverage -s '^ ' "$(basename "$TRAVIS_BUILD_DIR")"
 - raco cover -s main -s test -s doc -f codecov -f html -d ~/coverage . || true
 # TODO: add an option to cover to run the "outer" module too, not just the submodules.
 # TODO: deploy the coverage info.

scribblings/polysemy.scrbl

@@ -285,4 +285,8 @@ There are currently many limitations. Here are a few:
   have a notion of scopes (which could be used to hide some of these names), I
   do not see any way to avoid this problem, while still making simple imports
   (i.e. without renaming) work seamlessly with the stock implementation of
-  @racket[require].}]
+  @racket[require].}
+ @item{There is no support for polysemic identifiers in Scribble: identifiers
+  will not get highlighted, and @tt{raco doc-coverage} will complain that some
+  internal identifiers are not documented (using @tt{raco doc-coverage -s '^ '
+   module-path} is a quick workaround for this second issue).}]