Add missing closing parentheses in FAQ code snippet (#1052)

Author: sloede

docs/src/FAQ.md

@@ -34,7 +34,7 @@ Remember also that you should use the standard environment variables like `CC`,
 
 Yes!  You can use [`BinaryBuilder.runshell(platform)`](@ref BinaryBuilderBase.runshell) to quickly start a shell in the current directory, without having to set up a working `build_tarballs.jl` script.  For example,
 ```
-julia -e 'using BinaryBuilder; BinaryBuilder.runshell(Platform("i686", "windows")'
+julia -e 'using BinaryBuilder; BinaryBuilder.runshell(Platform("i686", "windows"))'
 ```
 will open a shell in a Windows 32-bit build environment, without any source loaded.  The current working directory of your system will be mounted on `${WORKSPACE}` within this BinaryBuilder environment.