Fix ToMap for tables in mixed-type arrays

[mstetson]

ToMap doesn't convert tables to maps if they're inline tables in a mixed-type array.

a = ["foo", { bar = "baz" }]

Before this change, ToMap will return a map where the second element of the array a will be a *toml.Tree instead of a map[string]interface{}.

[codecov]

Codecov Report

Merging #453 (2479d40) into master (5b4e7e5) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #453      +/-   ##
==========================================
+ Coverage   93.57%   93.60%   +0.03%     
==========================================
  Files          10       10              
  Lines        2257     2268      +11     
==========================================
+ Hits         2112     2123      +11     
  Misses        105      105              
  Partials       40       40              

Impacted Files	Coverage Δ
tomltree_write.go	94.80% <100.00%> (+0.19%)	⬆️

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[pelletier]

Awesome! Thank you for fixing this!