Bugfix for error found in tests

[stuvet]

Calling shiny::shinyAppTemplate(".") without library(shiny) throws the following error:

Error in HTML("\n\n\n
  test_that(\"Module values are consistent\", {\n  
     app <- AppDriver$new(name = \"mod\")\n  
     app$click(\"examplemodule1-button\")\n  
     app$click(\"examplemodule1-button\")\n  
     app$expect_values()\n
  })") :  
could not find function "HTML"

Changed to shiny::HTML

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[cpsievert]

Thank you @stuvet! I'd be happy to merge this once you've 1. accepted the CLA and 2. added a NEWS item.