Path to julia Appveyor (#329)

it seems the path to Julia has changed in Appveyor, to ```C:\julia\bin\julia```, so the readme should be adapted accordingly.

Co-authored-by: Max Horn <max@quendi.de>

README.md

@@ -198,7 +198,7 @@ When using Coverage.jl locally, over time a lot of `.cov` files can accumulate.
 
        ```yml
        after_test:
-       - C:\projects\julia\bin\julia -e "using Pkg; Pkg.add(\"Coverage\"); using Coverage; Coveralls.submit(process_folder())"
+       - C:\julia\bin\julia -e "using Pkg; Pkg.add(\"Coverage\"); using Coverage; Coveralls.submit(process_folder())"
        ```
 
 ## A note for advanced users