[minor] incorrect string handling in presence of quotes
nimble chokes on ` "example \"Nim to wasm\""`:
but correctly accepts ` "example \"Nim to wasm\" "`:

eg:
see https://github.com/2vg/nim-wasm-example at 8586a2d

```nim
# Package

version       = "0.1.0"
author        = "momf"
description   = "example \"Nim to wasm\""
# description   = "example \"Nim to wasm\" "
license       = "MIT"
srcDir        = "src"
bin           = @["nim_wasm_example"]


# Dependencies

requires "nim >= 0.19.0"

task installEmcc, "setup emscripten(install to <home directory>/emsdk)":
  exec "git clone https://github.com/emscripten-core/emsdk.git ~/emsdk"
  cd getEnv("HOME") & "/emsdk"
  exec "./emsdk install latest"
  exec "./emsdk activate latest"
  exec "source ~/emsdk/emsdk_env.sh"

task buildwasm, "build nim_wasm_example.nim":
  exec "nim c -d:release -d:emscripten -o:src/nim_wasm_example.js src/nim_wasm_example.nim"

task execwasm, "execute src/test.js":
  exec "node src/test.js"

task buildrun, "build and execute":
  exec "nimble buildwasm"
  exec "nimble execwasm"

task test1, "fake test1":
  echo "ok1"
```

nimble -v
nimble v0.11.0 compiled at 2019-12-17 14:12:58
git hash: 4007b2a778429a978e12307bf13a038029b4c4d9

```
nimble buildwasm
       Tip: 2 messages have been suppressed, use --verbose to show them.
     Error: Could not read package info file in /Users/timothee/git_clone/nim/temp/nim-wasm-example/nim_wasm_example.nimble;
        ...   Reading as ini file failed with:
        ...     Invalid section: .
        ...   Evaluating as NimScript file failed with:
        ...     Error parsing .nimble file: /var/folders/ll/dtd6ksrn50n3xkdy4y61tf_80000gn/T/nimblecache/nim_wasm_example_2619429263/nim_wasm_example.ini(4, 40) Error: invalid token: .
```
