Allow strings with "{" as modifier arguments

[cgewecke]

#478 (part II)

contract TestB is Interpolated {
    constructor(uint x) public Interpolated("abc{defg}") {
        uint y = x;
    }
}

[codecov-io]

Codecov Report

Merging #480 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #480      +/-   ##
==========================================
+ Coverage   99.23%   99.24%   +<.01%     
==========================================
  Files          20       20              
  Lines         784      790       +6     
==========================================
+ Hits          778      784       +6     
  Misses          6        6

Impacted Files	Coverage Δ
lib/registrar.js	100% <100%> (ø)	⬆️

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