v0.6.8

DSP v0.6.8

Diff since v0.6.7

Closed issues:

• I registered juliadsp.org (#354)
• Tukey win to rect method error (#364)
• Add support of non-0 Nyquist to fftfreq? (#370)
• Failure on julia 1.5 (#373)

Merged pull requests:

• Fix the footnote in iirnotch (#349) (@asinghvi17)
• Reject non-numerical arrays as arguments to conv (#360) (@fghzxm)
• Use Polynomials 1.0 API (#361) (@galenlynch)
• fix tukey window for alpha=0 (#365) (@1oly)
• Improve citation accuracy of citation [1]. (#368) (@PhilipLoewen)
• Update .travis.yml (#374) (@galenlynch)
• Expand compat with OffsetArrays to include v1 (#375) (@galenlynch)