Fix built in detection

[brummelte]

Variable names starting with a built in, will be detected as a built in.
So this does not work: +++formatNumber(123)+++. It is detected to use FOR.

notBuiltIns before change:

new RegExp(`^FOR`).test("FOR") // true
new RegExp(`^FOR`).test("FOR ") // true
new RegExp(`^FOR`).test("FOR\n") // true
new RegExp(`^FOR`).test("FORMAT\n") // true
new RegExp(`^FOR`).test("OTHER\n") // false

notBuiltIns after change:

new RegExp(`^FOR\\b`).test("FOR") // true
new RegExp(`^FOR\\b`).test("FOR ") // true
new RegExp(`^FOR\\b`).test("FOR\n") // true
new RegExp(`^FOR\\b`).test("FORMAT\n") // false
new RegExp(`^FOR\\b`).test("OTHER\n") // false

[coveralls]

Coverage increased (+0.01%) to 92.559% when pulling 756b9e7 on brummelte:patch-1 into eb0c8cf on guigrpa:master.

[jjhbw]

Awesome, thanks for noticing. I'll merge this in the staging branch and add some test cases for this behaviour.